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Famous mineral localities: the Castle Dome District, Yuma County, Arizona.

The Castle Dome district is one of the oldest and longest-lived mining district in Arizona. The Hull and Puzzler mines have produced attractive combinations of barite, cerussite, fluorite, unusual green vanadinite, yellow wulfenite and green mimetite.

INTRODUCTION

The Castle Dome mining district is located in southwestern Arizona, in the northwestern part of Yuma County. It is a relatively easy drive north out of Yuma on U.S. Route 95, and east on Castle Dome Mine Road across the Castle Dome Plains. The district lies in the Castle Dome and Middle Mountains, a linear geographic feature that parallels the northwesterly trend of the basin and range mountains of southern Arizona and northern Sonora. They are rugged and blocky, with steep rock spires and domed towers. Spilling out from boxlike canyons across the rock pediments are bajadas surrounded by alluvial plains.

The origin of the name "Castle Dome" used throughout the area is believed to be a corruption of "Capitol Dome," a high, dome-like peak nearby which was named by American soldiers at old Fort Yuma in the 1880's. Early Spanish explorers called the same peak Cabeza de Gigante, "Giant's Head." But portions of the area also resemble the stockades and turrets of medieval castles.

LOCATION

The 7 1/2-minute Castle Dome Peak quadrangle, Arizona, locates the Castle Dome district at T4S, R17W to R19W. The district lies within the Kofa National Wildlife Refuge and north of the U.S. Army's Yuma Proving Ground. The mines are clustered and scattered along a southeast-northwest trend covering about a four-square-mile area. Castle Dome Mine Road terminates in the central part of the district, near the Castle Dome mine itself. Other mines in the district can be reached by dirt roads or jeep trails, or on foot from the wash bottoms.

Elevations vary from about 1,300 feet in the low-lying areas to 1,600 feet along the ridges. Castle Dome Peak rises to an elevation of 3,788 feet. Vegetation is desert scrub. The area lies within the Lower Colorado Valley vegetation zone of the Sonoran Desert. As one might expect, temperatures are severe in the summer, commonly over 100 [degrees] F for long periods of time. Because of the extensive network of arroyos and the wide-spreading bajadas, flooding in the low-lying areas is common during the summer rainy season.

HISTORY

The Castle Dome mining district is among the oldest and most continuously worked mine groups in Arizona. William P. Blake, an early Arizona mineralogist and president of the Castle Dome Mining and Smelting Company, wrote about the early history of the mine in an 1880 company report:

Exactly who did the earlier work and when is not clear. It was in 1863. however, that two miners named Conner and Snively came upon galena ore that they assumed was pure silver. While there was indeed silver in the ore, it only amounted to about 30 ounces per ton. The ore was hand-sorted and sacked, then hauled by wagon to Castle Dome Landing on the Colorado River. River boats took the ore to clipper ships in the Gulf of California, where it was shipped to the Selby smelter in San Francisco.

In 1864, just a year after the first claims were staked, J. Ross Browne traveled through the area and reported on what he saw:

In 1868, production records note 60% lead and $40 per ton silver, with an overall ore value of $90 per ton. It was also noted that costs to mine and sack the ore were $12 per ton, $15 to haul it. and $18 to ship it to San Francisco. Investors were doubling their investment. In 1875, a smelter was built in Yuma which handled the Castle Dome ore until the following year. In 1876, the Southern Pacific Railroad across Arizona made transport of the ore to San Francisco more economical. The Yuma smelter shut down, and ore was once again sent to the Selby smelter.

The Buckeye Vein Group, which includes the Castle Dome mine, was patented in 1876, with much of the work done before 1890. Ore shoots were stoped to the 250-foot level from inclined shafts. The Hull (Rialto) Mine Group saw its greatest production from the years prior to 1900, with about 20,000 tons of ore recovered from stopes to the 200-foot level.

Ownership and production changed hands several times over the next few decades. In the late 1870's, the Castle Dome Mining and Smelting Company was organized; they shipped ore to Melrose, California for processing until 1883. From 1890 to 1896, ownership was in the hands of Gondolfo and Sanguinetti, who resumed ore shipment to Selby.

The majority of the later work in this century came from reworking old fills and dumps, with some underground mining in the old mines. All together, lead and silver ore totaled about 119,000 tons, containing 10,500 tons of lead, 478,000 ounces of silver, 38 tons of zinc, and some copper and gold byproducts. During 1902-1904, 1908-1909, and in 1913, a considerable amount of fluorite was sent to Riverside Portland Cement in southeastern California. From 1916 to 1918 the mines were worked for potash recovery.

It was not until the 1940's that the mines at Castle Dome began producing again. At that time, most claims were owned by Mrs. Eliza De Luce and leased by brothers George and Kenneth Holmes. They had a payroll of 20 people. Mining included underground work in six shafts, identifying reserves of 40,000 tons of ore. They had also produced 2 million pounds of lead and 27,000 ounces of silver from concentrates realized from dump ore and stope fill. Development included an additional 600-foot shaft and a diamond drilling project to explore for deeper deposits and parallel veins.

The idea was to ship 200 tons of ore a day to a mill on the Gila River 25 miles distant. But times were tough, as shown by a series of memos and letters between the brothers and ASARCO in El Paso, seeking payment on a shipment worth about $830 for 30,277 pounds of lead from the mines in late 1942. The Holmes brothers listed the following expenses for operating the mine: $0.75 per hour to muckers, $0.80 to miners, $0.85 to timbermen, all with time and a half for overtime; $2.50/ton to draw and hoist ore, $1.25/ton to haul from mines to mill, $0.75/ton for milling, and $2.50/ton to recover 30% lead from concentrates during smelting. Not only were costs to run greater than expected, but road conditions were mining their trucks, and the price of lead was not high enough to allow much of a profit. The operation shut down again in 1944 after producing 3 million pounds of lead.

In the 1950's, the U.S. government recovered low-grade manganese ore from the andesite volcanics in the area, which produced 400 tons of 26%-30% manganese. Various concerns operated the mines sporadically from 1978 to 1982. Copper production from the Castle Dome mines was minimal, mostly at the Copper Glance mine. In the 1970's about 150 tons of ore produced 9 tons of copper, 1,465 ounces of silver, and minor gold and lead.

Gold, in combination with silver, was a byproduct recovered from the Castle Dome ores. Gold had been known in the area as far back as the 1860's, but the only records are from 1884, when it was noted that gold had been recovered from placers by Mexican dry washers. The placer deposits in gravels at or near bedrock in gulches are thought to have come from gold-bearing veins near the Buckeye mine. Serious mining for gold and silver did not begin until about 1912; a total of 2,380 tons of ore was mined, containing 2,150 ounces of gold and 19,000 ounces of silver. The total ore production of the Castle Dome district up to 1912 amounts to more than $2 million in lead, silver, gold, zinc and copper.

Mining in the district was accomplished in open cuts, and by stoping of veins reached by numerous shallow shafts. The area produced from 1863 until the mid-1980's, with some minor "weekend prospecting" going on to the present time. Roughly 120,000 tons of ore came from the district, containing 10% lead, 5 ounces per ton silver, placer and lode gold, and minor copper and zinc. Fluorite was, apparently, the only significant industrial mineral recovered from the Castle Dome district.

COLLECTING HISTORY

Though the Castle Dome district has an extensive history of mining and a significant suite of secondary minerals, good mineral specimens have never been plentiful. They were as rare on the specimen market 40 years ago as they are today (Scott J. Williams, personal communication). However, this is not due to collectors being unaware of the district or indifferent to it. Quite the contrary, specimen collectors have been scouring the dumps and underground workings for more than 50 years. The more likely reason, with few exceptions, is that significant quantities of specimen-grade material just don't occur in the Castle Dome orebodies.

The earliest recorded specimen from the Castle Dome district is in the University of Arizona collection in Tucson. It is labeled "Anglesite with galena, cerussite and [fluorite], Castle Dome, Arizona." Professor William P. Blake, who taught at the University from 1895 to 1905, donated the piece. He published well over a dozen professional works on the geology and mineralogy of the Arizona Territory and had a special interest in the Castle Dome mining district. Several of his publications dealt with the district, and he was president of the Castle Dome Mining and Smelting Company for a period in the late 1870's and early 1880's. It isn't known if Blake personally collected the piece now in the University of Arizona collection but, given his involvement in the district, it is a strong possibility, especially since he states (1881a) that he personally collected specimens there in the spring of 1880 and 1881. There is no further indication of specimen recovery until the late 1940's.

1950-1970

The earliest known efforts at specimen recovery involved Billy Theison and her first husband, Darrell Casey. The Caseys lived in a small house nestled in a narrow valley just east of the Puzzler mine from 1949 to 1969 (Billy Theison, personal communication). Darrell was a civilian employee at the nearby Yuma Army Proving Ground. Billy loved minerals and had a passion for exploring. She scoured mine dumps and, where possible, searched the underground workings in her pursuit of minerals. They maintained a small shop by their house where she sold some of the things she had found.

Many collectors that visited the district in this period developed close friendships with Billy and received their introduction to the mines from her. The minerals they collected consisted primarily of vanadinite from the Puzzler and Silver Cross mines, wulfenite from the Puzzler and Hull (Rialto) mines, cerussite from the Hull mine, and fluorite from the Hull, Senora and some of the smaller unnamed workings.

The late William Sanborn collected the district extensively in the 1950's and 1960's and was one of the more successful collectors of this period. Much of his collecting was done with Billy. They did extremely well at the Puzzler mine, collecting many flats of greenish brown vanadinite to 6 mm on black manganese-stained calcite matrix (Billy Theison and Gene Tribbey, personal communication). They also collected a few flats of yellow wulfenite occurring as clusters of crystals to about 6 mm. Specimens from the Puzzler dating to this period probably came from Bill and Billy. Bill is also reported to have done well collecting yellow wulfenite on fluorite and cerussite at the Hull mine.

Bob Pedersen is a field collector living in Tucson with over 35 years of experience collecting the Castle Dome mines. Most of his time in the district has been spent at the Hull mine. In addition to the wulfenite and cerussite specimens typical of the mine, Bob found specimens of wulfenite with unusual green mimetite in the late 1960's. The occurrence was on the 260-foot level and was very limited, producing only a few pieces. The mimetite occurs as bright, translucent, yellow-green balls to 3 mm with gemmy, lemon-yellow, "window pane" wulfenite crystals to about 5 mm. Most are thumbnail size, although Bob did get one piece about 8 cm across which is still in his collection.

1970-1985

Around 1970, Bill Sanborn showed Jack Crowley through the district, taking him to many of his favorite collecting areas (Jack Crowley, personal communication). Jack reports that Bill lamented while on these trips about the deteriorating condition of many of the mines. Some of his favorites had become inaccessible due to dangerous conditions. Jack continues to collect the area today whenever possible. He feels his best finds have been wulfenite from the Hull mine, vanadinite from the Puzzler mine and some interesting diagonally zoned fluorite from some small workings in the eastern part of the district. The fluorites form bright 2.5-cm cubes that are zoned green and purple.

From the mid-1970's through the mid-1980's the high price for silver generated a renewed commercial interest in the mines, the Hull mine in particular. While collecting was still possible in some smaller outlying properties, for the most part the main ones were off-limits. Peter Megaw, Kurt Gilliam and Stan Esbenshade collected good quality cubic fluorite crystals to 2.5 cm from some small shafts in the southern end of the district around 1980-1982. The fluorite has an attractive blue-green color with good clarity and luster; many crystals occurred on matrix. Some of the better pieces from their find are today in the collection of the Arizona-Sonora Desert Museum in Tucson.

1985 to the Present

As might be expected, when mining operations ceased in the mid-1980's field collectors descended on the district en masse. In addition to those already mentioned, these included Ray Grant, Graham Sutton, Fred DeVito, Ron Gibbs, Malcolm Alder, Ken Algier, Mitchell Dale, Paul Bakerman, George Stevens, George Godas, Dick Morris and Mark Hay. Many of these collectors made significant finds.

Today most of the mines of the Castle Dome district are inaccessible. Shafts that once provided entry are impassible, their timbers and ladders have collapsed, leaving only intimidating black holes, inaccessible to anyone other than technical rock climbers. The mines that are the heaviest collected today are the Hull and the Puzzler, largely because they remain accessible. Additional collecting is possible in the numerous shallow shafts and prospects that pepper the district.

Collecting in the district over the last 10 years is related below through the personal experiences of one of the authors (MH). Mark, along with friends Dick Morris and George Godas, has spent much time collecting in the district, primarily at the Hull and Puzzler mines and some of the shallow unnamed prospects in the southern part of the district.

Hull Mine

Our first trip to the Hull mine was in 1987. George Godas, Dick Morris and I were digging a seam of cerussite that Ray Grant had discovered a few years earlier. The seam was in the face of a short dead-end drift on about the 250-foot level of a large, inclined tunnel that had been driven in the 1970's. It was producing euhedral cerussite crystals in the 6-12 mm range, though a few reach 2 cm. The cerussite occurred as waxy, dipyramidal sixlings on a fine-grained, greenish gray volcanic matrix with occasional bright orange, small ([less than]1.5 mm) pseudocubic wulfenites and cemented fragments of barite and fluorite. Over the next year or so, about a dozen flats of specimens ranging in size from thumbnail to cabinet were collected. An excellent small cabinet specimen from this find is in Les Presmyk's collection (Gilbert, Arizona). Additional good pieces can be found in the Arizona-Sonora Desert Museum and the Tucson Gem & Mineral Society collection. This seam was probably the most prolific producer of good quality specimens found in the Hull mine in recent years.

The new tunnel mentioned above bottoms out at about the 300-foot level, where it breaks into an old stope. The stope is largely backfilled with muck and is extremely dangerous. We never had the courage to venture far into it. In the right rib of the tunnel, just before the old stope, is a large crack that runs perpendicular back into the rock and up. It twists out of sight and appears to be totally barren of minerals. However, several thick, yellow, tabular wulfenite crystals to about 1.2 cm were found buried in the loose sand in the floor of the crack. These are nice, but they always occurred as singles, no groups and never on matrix. On one trip Dick dug an unusual cerussite crystal out of the crack. The cerussite is odd in that it is not the usual dipyramidal sixling; instead this one is a heavy, thick, reticulated group about 3.8 cm long. It's the only one of this type we ever found at the Hull. We tried to dig the crack back to the mother lode that was certainly just out of sight but the rock was extremely hard. We began by working the crack but, after a couple of hours and no noticeable progress, we moved off in search of easier digs!

In 1989 and 1990 George, Dick and I dug in an area on the 100-foot level where the new tunnel intersects one of the old shafts. When the mine was operating in the 1970's the shaft was retimbered and used as a fire escape route. George had discovered a way to crawl under the wooden flooring near the shaft where there was a rich galena seam in the vein. Occasionally a vug could be found with bright orange, pseudocubic wulfenites to 6 mm; they strongly resemble Los Lamentos wulfenite in both form and color. Wolfgang Mueller collected a few wulfenite crystals to 1.2 cm several years before, from the shaft wall just below this area. The wulfenite sometimes occurs on euhedral galena crystals coated with a fine-grained, sugary cerussite and sometimes accompanied by pale blue-green, transparent cubes of fluorite. All in all, the specimens are very attractive.

George and Wolfgang entered the lower workings by way of the fire escape shaft in the summer of 1990. They found strong showings of wulfenite, cerussite and fluorite but again with difficult digging conditions. The most interesting pieces they collected are several thumbnail-size specimens showing small lemon-yellow wulfenite crystals with bright yellow-green mimetite balls. They were probably found very close to where Bob Pedersen found his 25 years earlier. George said conditions were very difficult but, with work, he thought there was a reasonable chance of collecting more pieces with the wulfenite/green mimetite combination. However, shortly after their trip the fire escape shaft burned and all of the timbers and ladders destroyed.

Puzzler Mine

Some of the most exciting and satisfying mining trips I've ever had were at the Puzzler mine. Dick Morris, George Godas and I first went there in July 1987. At the time the place was a total mystery. We had only seen a single specimen and had not found any Arizona field collectors who had been there; most had never even heard of it. Like many mines in the Castle Dome district, it wasn't identified on the topographic maps. However, we were fortunate enough to find a claim map at the Arizona Department of Mineral Resources that located the Puzzler claim. By comparing the water drainage patterns on the claim map with those shown on the topo maps we were able to narrow it down to just a few mines.

We split up and it was George who actually found the mine first, tipped off by vanadinite on the dump rock. There was a weathered old flat-bed mine car chained in place straddling the shaft. By pushing the car to the side there was just enough room to squeeze our heads through and look down inside. It was a vertical shaft, obviously quite old but the timber looked in reasonably good shape. A weathered wooden ladder disappeared down into the darkness. This definitely predated Federal MSHA safety regulations. The ladder looked like railroad tracks going to the horizon, except these went straight down as far as the eye could see.

Going in the first time was quite a thrill. We had to go in backwards, squeeze past the mine car, then with our butts hanging out over the shaft, find the ladder with our feet. There was a strong sense of relief when that first rung was located! To be "safe" we tied off a rope and threw it down beside the ladder. How we were going to grab the rope in the split second it would take for the ladder to fail was a mystery but we all felt better having it there.

Conditions underground suggested that it had been many years since anyone had been in the place. There were newspapers dating to the 1960's, and Saturday Evening Post magazines from the 1930's. But the strange thing was the tools. Gads, chisels and pry bars lay about like the diggers might have just gone out for lunch and would be returning any minute! It was peculiar but it gave us a strong connection to those that had been there before. We didn't know who they were or when they had been there but we knew very well what had motivated them.

Everywhere we looked were glittering tiny yellow-brown crystals! The amount was truly astonishing. The shaft was sunk right down the vein, and its walls glistened with vanadinite. The many cracks and fissures in the walls sparkled with thousands of tiny prisms. Needless to say, we went nuts! We filled our flats in record time and headed out to the truck for more. At the surface we inspected our treasure and discovered that all that glittered was not glorious. When examined in the full light of day, we found our flats to be filled with the ugliest vanadinite we'd ever seen, seriously ugly. (It's an experience common to underground collectors - in a dirty black hole a simple mine light has a remarkable ability to make an ugly rock look wonderful.) Even with this early setback, though, the potential was obvious: the Puzzler was ripe for a choice pocket.

Over the next two years we put in many hundreds of hours of hard work. Our efforts produced small finds of yellow wulfenite plus cerussite and anglesite as microspecimens. Fluorite was common, occurring mostly as unconsolidated breccia fragments within the vein structure, but collector-grade specimens were extremely scarce. It was the vanadinite, however, in various forms and colors, that gave us our best finds - several hundred flats' worth - mainly from three large pockets.

The first pocket was hit by Dick and myself on New Year's Day 1988. It was on the 180-foot level, midway down the south tunnel. We were following a highly fractured seam into the ceiling when it opened into a pocket about 45 cm tall, 60 cm long and up to 10 cm wide. We have always referred to this as the "Green Pocket" because of the jade-green color of the crystals. We were stunned; their appearance was strongly suggestive of pyromorphite. If so, they were the finest we had ever seen from Arizona. We subsequently gave a sample for analysis to Chuck Lewis at Arizona State University, and he confirmed it to be vanadinite.

The Green Pocket produced about 10 flats of material. Specimens range in size from thumbnail to about 18 cm, most occurring as dense crusts of vanadinite crystals on matrix. The crystals have brilliant luster and curved, barrel-shaped sides. Individual crystals reach a maximum size of about 5 mm, but they often appear larger due to a propensity to occur in subparallel groups.

An unusual aspect of vanadinite from this pocket, both in terms of other pockets from this mine and other Arizona occurrences in general, is their tendency to form stacks of crystals which rise off the matrix in curving subparallel growths. Some are as much as 2.5 cm tall. The curve to these stacks is always convex upward with smaller crystals on the bottom and larger on top. These are very similar in habit to some of the curved pyromorphite crystal groups from Kellogg, Idaho.

Many of the pieces recovered from the Green Pocket occur with barite in delicate white, tabular crystals and rosettes of crystals to 6 mm. Four years later, in 1992, George collected some wonderful barite crystals from the floor near the Green Pocket. His barites are also white but are up to 5 cm on a side and are lightly dusted with small (1 mm), bright orange-yellow vanadinite crystals. George recovered about a dozen high-quality specimens from his pocket.

The second vanadinite pocket also occurred on the 180-foot level, but at the other end of the mine, north of the shaft. Here the tunnel ends in a pile of rubble where it intersects the bottom of a large stope. In the tunnel ceiling just before its end, Dick and I opened a large pocket of hoppered caramel-brown vanadinite. The crystals have excellent luster and measure up to 1.2 cm, on plates as large as 40 cm across. These specimens are particularly appealing because of an epitaxial growth of small vanadinite crystals perched at the ends of the larger crystals on some of the specimens. The smaller crystals are attached at the point formed by the intersection of adjacent prism faces and the c-face termination of the larger crystals. This pocket produced the largest crystals and the largest specimens we ever obtained from the Puzzler mine. Overall, about six flats were recovered.

The third pocket we refer to as the "Winze Pocket" because we found it at the bottom of a short underground shaft (a winze) at the south end of the 100-foot level. The winze is only about 15 feet deep and, like the main shaft, was sunk right on the vein. The Winze Pocket was not really a pocket but a long seam that was loaded with vanadinite crystals. We never worked the seam to its end. It seemed content to produce specimens as long as we continued to work. This was the most prolific zone for good specimens we found in the Puzzler.

The seam extended both north and south from the winze. However, the best vanadinite was to the north. Dick and I worked it for several months in the late spring and summer of 1998, handdigging a new tunnel for 3 to 4 meters along the seam. Crystals are simple hexagonal prisms with flat c-face terminations. They attain a maximum length of about 6 mm. The best crystals are dark greenish brown with rich orange terminations and a brilliant, adamantine luster. The matrix is totally coated with small, bright yellow-green crystals that contrast nicely with the larger dark crystals. Other pockets commonly yielded a half dozen to a dozen flats of nice pieces, but the Winze Pocket produced 60-80 flats. The winze has since become almost totally filled with muck; the seam is still there and could produce more good specimens but it will require a lot of work to get to it.

Unnamed Prospects

Our most recent efforts in the Castle Dome district have focused on a search for a good fluorite locality. Dick and I had been searching Arizona for a fluorite dig for several years. The Castle Dome area is known to be especially rich in fluorite and was an obvious target. Finding a Castle Dome mine with good fluorite potential is easy; the challenge is finding one that is accessible.

In November 1995 Dick and I located a strong northwest-southeast trending vein in the southern part of the district with a tremendous showing of fluorite. We walked it for over a mile and found small location pits every few hundred feet, each with a tiny dump littered with fluorite fragments. We continued to trace the vein south and came on the workings of the Senora mine. The dumps of the Senora were totally covered in lavender, pink and colorless fluorite, some with terminated cubic faces to 2.5 cm. Clearly an enormous amount of fluorite was present underground. But, as is often the case in this district, the only access was via the vertical, untimbered shafts. For us, at least, that rendered them inaccessible. A short distance south of the Senora the vein appears to pinch out and no more workings are seen.

This was clearly an exceptionally rich area and we continued our search, checking smaller veins to the east and west. We soon located a small prospect shaft on a parallel vein about 60 meters to the east of the Senora vein. The shaft was about 12 meters deep and its dump was covered with rocks composed of breccia fragments cemented together with fluorite. In the cracks and holes between pieces we found razor sharp fluorite cubes to almost 2.5 cm.

The shaft was untimbered and almost vertical but it was relatively shallow so we were able to get into it using simple rope ladders. The biggest hindrance was a thick carpet of cholla cactus spines coveting the floor of the shaft. We shoveled as many as possible into the corner and covered them in rock but we still spent time after each trip picking cholla needles out of our hands and knees (and other places).

Climbing down the shaft we saw that the walls were absolutely loaded with fluorite and barite; there were several pockets exposed and waiting to be collected. It appeared that this prospect had been completely overlooked by other collectors! The pockets were lined with large, dark blue-green fluorite cubes in places intergrown with milky, thick, tabular barite crystals. Both the barite and the fluorite in the exposed pockets were heavily fractured and most cleaved or broke when we tried to collect them, but we were still able to get some nice single crystals. Dick and I visited this little shaft many times over the next few months, each time returning with six or eight flats of specimens.

We found several pockets by digging in the walls of the shaft. The largest probably measured about 45 cm long by 25 cm high by 10 cm wide. In many cases the pockets were filled with silt and clay. In these pockets, the fluorite crystals had become detached and were floating in the silty fill material. Their bases were broken where they had come loose from the wall rocks but their edges and faces were surprisingly undamaged. Unfortunately, all of the crystals in these pockets were coated in a thick layer of caliche and, thought the color was good, they lacked good luster. However, we found a few pockets that were not filled with dirt. In these pockets the fluorite crystals were clean and had excellent luster. The crystals always occurred as extremely sharp cubes with absolutely no crystallographic variations. They are up to 6 cm across and range in color from a pale, watery green to a rich, deep blue-green. Many of the smaller crystals were obtained on matrix but, of the larger ones (those greater than 2.5 cm across) only a few came out on matrix.

In addition to the fluorite, barite and rarely galena also occur in the mine. The barite is found as large, thick, tabular, milky crystals often totally filling the pocket. In these instances, the barite crystals rendered the pockets virtually worthless. The barites were so tightly packed they just broke up when collected. We recovered crystal fragments up to 10 cm long and over 6 mm thick but only rarely would even one end be terminated. The fluorite crystals lining these pockets were usually ruined as well, due to damage resulting from contacting the barite. The galena, on the other hand, while not particularly aesthetic, was interesting and always a thrill to find. They occur as cuhoctahedrons up to 5 cm across, usually as individuals nestled down in among the fluorites. In all cases, the surface of the galena crystals has altered to a fine-grained, sugary coating of anglesite and cerussite.

We revisited the little shaft in the spring of 1997 and were disappointed to find that it had been filled with muck to within 5 feet of ground surface, apparently by collectors digging fluorite and barite in the vein material around the collar of the shaft.

GEOLOGY

Geological investigations in the Castle Dome district have been going on for more than a century (see Wilson, 1933, 1951; Gutmann, 1981, 1982; etc.). William P. Blake compiled reports that date back to the late 1870's. He notes, as geologists continue to do at present, some unmistakable geologic features. The northern part of the Castle Dome Mountains is a thick sequence of Cretaceous to Quaternary volcanics in excess of 2,000 feet in thickness. They are mainly extrusive rhyolite, andesite, tuff and obsidian, with the oldest cut by quartz porphyry dikes. The oldest extrusive rocks are capped by a Quaternary basalt flow several hundred feet thick.

In the southern part of the mountains, the rocks are metamorphosed sedimentary and intrusive igneous rocks. Schist and gneiss of Mesozoic age also occur in fault contact with Cretaceous sedimentary rocks (shale, cherry limestone, arkosic sandstone, conglomerate) and metamorphic quartzite and slate. The sedimentary rocks are dissected extensively by a diorite and rhyolite dike swarm. The rhyolite is younger than the diorite, which is believed to be older than the extrusive volcanics. Finally, on the eroded Mesozoic rocks and Cretaceous sediments there is a series of extrusive rocks which consist of andesite, rhyolite flows and tuff.

The alluvial plains surrounding the Castle Dome Mountains consist of a thin veneer of sediments overlying a Cretaceous (maybe Tertiary in some areas) basaltic cap. The alluvium fans out in bajadas from the canyon mouths to the west over the Castle Dome Plains.

The structure of the mountains is dominated by a series of northwest-trending faults occurring along the northern and northeastern part of the range, and in the extreme southern end. The faults are near vertical and tilt the volcanic units 7 [degrees] to the east. These faults have been intruded locally by Laramide-age granite, syenite, diorite and quartz porphyry. The majority of the mineralization in the Castle Dome district occurs within these dikes.

The deposits are believed to have formed as a result of hydrothermal deposition from a very deep magma source. The nature of the mineralization suggests deposition occurred in the mesothermal zone, meaning the deposit formed about 4,000 feet below the land surface at the time of deposition. Ore deposits consist of argentiferrous galena replacements along fissure veins through most of the district, and placer gold and gold-bearing veins in the area around the Buckeye mine.

MINES

Hull Group

The most important mines and workings in the district (Wilson, 1933) fall into eight general groups, beginning on the north with the Hull (Rialto) group, situated along the Hull vein which strikes N30 [degrees] W and dips 65 [degrees] to 75 [degrees] NE. Northernmost in the group is the Chief of Dome, followed southward by the Hull mine (two shafts), the Diana (five shafts) and the Surprise (four shafts). Underground workings have exploited the vein for more than 2,000 feet in stopes up to 18 feet wide extending to a depth of up to 275 feet.

Cleveland-Chicago Group

The Cleveland-Chicago vein runs roughly parallel to the Hull vein, apparently beginning south of the Diana shafts at the Lucinda mine and extending southeasterly. The Algodones mine is next along the extended trace of the vein, followed by the Cleveland mine (two shafts) and on to the Chicago mine (several shafts). The vein is clearly traceable between the Cleveland and Chicago shafts for at least 1,400 feet, where it strikes S30 [degrees] E and dips about 80 [degrees] W. A considerable portion of the vein above the 100-foot level has been stoped.

Buckeye Vein

Claims along the Buckeye vein begin just northeast of the middle of the Flora Temple vein, with the old Castle Dome claim (at least seven shafts, patented in 1876) and follow the trace of the vein for about a mile southeast. After the Castle Dome shafts come the New Dil, Lady Edith, Yuma (three shafts) and Big Dome (four shafts) mines. The vein here dips about 70 [degrees] W. The New Dil and Lady Edith sections of the vein were stoped out continuously for a distance of more than 1,000 feet, and to a depth of 250 feet.

Little Dome Vein

South of the Flora Temple vein is the Little Dome vein, which adjoins the Senora vein on the north end and extends along strike through four shafts to the southeast. The vein strikes S45 [degrees] to 55 [degrees] E and dips 85 [degrees] SW. Stopes 4 to 7 feet wide follow the vein for a length of 125 feet and to a depth of 20 to 60 feet.

Senora Vein

The Senora mine (at least three shafts) begins at its northern juncture with the Little Dome vein and traces southward, curving toward the east and ending at the Union and Lincoln mines. The Senora vein strikes N20 [degrees] to 40 [degrees] W and dips 50 [degrees] to 70 [degrees] E. The vein has been stoped out to a width of up to 5 feet, and to a depth of 300 feet. Below the 250-foot level the vein pinches to only a few inches in thickness. The southernmost two shafts are connected underground by stopes.

Mabel-Adams Groups

South of the Chicago mine about half a mile are the Mabel claims (five shafts), and adjacent due south from there are the Adams claims (at least four shafts, of which the Puzzler is by far the most important). Most of the stoping in the Mabel mine took place south of the shafts toward the Adams claims, on an 11-inch streak of galena that feathered out with depth; workings extend down to 380 feet. In the area of the Puzzler mine the vein strikes S23 [degrees] E and dips 70 [degrees] NE; in places the stoping is 7 or 8 feet wide. Very little drifting has been done on the other shafts in the Adams group.

Flora Temple Vein

The Flora Temple mine has the distinction of being the second claim ever patented in Arizona (in 1871). At least 11 shafts along two semi-parallel veins are connected underground by a series of stopes. For many years the Flora Temple was the most important producer in the district, and its workings are probably the most extensive. The veins have been stoped out to a width of up to 10 feet and a depth of 225 feet for most of the 2,000-foot length of the claim. The veins strike N18 [degrees] W and dip 45 [degrees] to 55 [degrees] E.

Colorado Vein

Claims known as the Lincoln or Colorado Group were located about 5 miles southeast of the Union mine at the extreme southern end of the district (Crampton, 1919). The vein here strikes northerly and dips about 45 [degrees] W; it measured 1 to 3 feet thick in most places, occasionally widening to 8 feet. The high-grade argentiferous galena and cerussite were accompanied by calcite, a small amount of barite, and economic quantities of fluorite sometimes shipped as ore. These claims were all owned by Althee Modesti, a Yuma merchant; the Colorado was worked single-handedly on a lease by Juan Laguna from 1898 to 1904, using only hand tools. Johnson (1911) states that "at the lowest level reached in the mine some very rich [silver] chloride ore was cut."

MINERALOGY

The most important mineral deposits of the Castle Dome district are the veins of argentiferous galena emplaced along several major fissures. The principal gangue minerals are fluorite and calcite with quartz, aragonite and late-stage barite. There is little copper in the district. Collectible secondary minerals are primarily the product of alteration of the galena, first to anglesite, cerussite and minium, and then to the more attractive vanadinite, mimetite and wulfenite. A little zinc is represented by smithsonite and hydrozincite lining vugs and watercourses. Perhaps the most unusual collector-quality species (for Arizona), aside from the green vanadinite, is the attractive, pale green fluorite found as crystals lining fissures and often with associated vanadinite and wulfenite.

Anglesite PbS[O.sub.4]

Anglesite was first reported from the district by J. G. Brush (1873), who chemically analyzed a compact variety, and later by Foshag (1919) and Wilson (1933). Foshag described "very showy specimens" of 1-cm yellow wulfenite crystals scattered over etched crystals of anglesite as superficial alteration layers surrounding cores of galena. At the Senora claim cubical pseudomorphs of black anglesite after galena crystals were found, sometimes coated by a film of rusty-red minium. At the Flora Temple claim anglesite/cerussite-coated alluvial nuggets of galena in gravel were traced to their source veins. Some anglesite has a "woody" appearance. Small crystals 3 to 6 mm in size have also been collected at the Puzzler mine.

Aragonite CaC[O.sub.3]

Anthony et al. (1995) report aragonite in the district in channels and vugs associated with smithsonite, hydrozincite, wulfenite, vanadinite and mimetite.

Barite BaS[O.sub.4]

Foshag (1919) reported barite from the district as platy masses and also rarely as large, clear crystals in open cavities. Wilson (1933) notes it as a common gangue mineral in the argentiferous galena-fluorite veins, as massive vein fillings and as groups of bladed crystals. At the Senora claim, at least, the barite is clearly later than the fluorite; at the Little Dome claim veinlets of crystalline barite cut across crystalline fluorite and calcite.

Cerussite PbC[O.sub.3]

Wilson (1933) reported cerussite as a common constituent of ore, forming alteration layers around nodules of galena. Anthony et al. (1995) mentioned sixling twins from the Hull mine. These are solid pseudohexagonal dipyramids up to 1 cm each or more, sometimes in connected groups and clusters. Associations include minium, litharge, anglesite and other secondary lead minerals. Some nice microcrystals have also been collected at the Puzzler mine.

Chalcocite [Cu.sub.2]S

One specimen in the Smithsonian Institution (#65493), labeled as originating in the Castle Dome district, contains chalcocite with malachite. This may, however, be from the Thumb Butte district, 6 miles south of Castle Dome, where veins of chalcocite and malachite were mined from 1918 to 1929 (Wilson, 1933). The principal mine of the group was the Copper Glance.

Descloizite Pb(Zn,Cu)(V[O.sub.4])(OH)

Guild (1910) reported Castle Dome as being a "well-known" locality for descloizite on wulfenite, vanadinite and calcite.

Fluorite Ca[F.sub.2]

Fluorite is a common gangue mineral in the argentiferous galena veins of the district. Foshag (1919) reported it in green masses and commonly as green crystals which, if exposed to sunlight, take on a pale pink hue. Crystals of blue to purple color are also known. Ladoo (1923) described a photosensitive black fluorite from the Hull mine which changes to a pale gray or pink color on exposure to sunlight. At the Senora mine Wilson (1933) reported pale green, purple and rose-colored crystals from "less than an inch up to several inches in diameter." At the Adams claims greenish fluorite crystals to an inch in diameter were found. Cubic crystals to 3 inches on an edge, with multiple phantoms, have been collected at the Hull mine; some are sprinkled or coated with small wulfenite crystals.

Freieslebenite AgPbSb[S.sub.3]

Anthony et al. (1995) report that a small amount of freieslebenite was mined from one of the claims in the district and was shipped with other argentiferous ores.

Galena PbS

Galena, much of it argentiferous, was the principal ore mineral of the galena-fluorite veins in the district, including the Flora Temple, Senora, Little Dome, Hull, Lincoln and Adams properties. Masses and crude cubic crystals were once quite common, as well as cubical pseudomorphs of black anglesite after galena. In places nearly solid vein fillings of galena up to 8 feet thick were mined (Blake, 1880). Some remarkable cubic crystals up to 4 cm on an edge and coated with white drusy anglesite-cerussite have been collected from a shaft at the southern end of the Senora vein.

Gold Au

Gold-bearing veins were found in the eastern portion of the Castle Dome Mountains. Only the Big Eye vein, about 4 miles south-southeast of Castle Dome Peak, had any production; it operated from 1912 to 1917, yielding about $33,000 in gold. Including local placers plus a few byproduct ounces from the Copper Glance mine, 6,556 ounces of gold were recovered from the district (Wilson, 1933), half of that by dry-washing from 1884-1908. The lead-silver veins in the district have not yielded any gold.

Gypsum CaS[O.sub.4][multiplied by]2[H.sub.2]O

Massive and crystalline gypsum is commonly found in the upper portions of lead-silver veins in the district (Wilson, 1933).

Hydrozincite [Zn.sub.5][(C[O.sub.3]).sub.2][(OH).sub.6]

Hydrozincite with minor gypsum is found in the upper portions of all veins, especially on the Senora claim, mainly in solution channels. Other associated minerals in these channels include calcite, cerussite, smithsonite, wulfenite, vanadinite and mimetite (Wilson, 1933). The hydrozincite is fluorescent (Flagg, 1958).

Mimetite [Pb.sub.5][(As[O.sub.4]).sub.3]Cl

Mimetite occurs in vugs and solution channels in association primarily with wulfenite. Yellow crystals of wulfenite at the Hull mine have been found on botryoidal, dull-green to yellow-green mimetite [ILLUSTRATION FOR FIGURE 33 OMITTED]. Blake (1881a) noted vanadiferous mimetite, as "crusts of small aggregated crystals of a light brown to straw-yellow color and waxlike luster."

Minium [Pb.sub.3][O.sub.4]

Minium, a powdery red lead oxide, occurs commonly in the district where galena is altering to anglesite and cerussite (Wilson, 1933).

Torbernite Cu[(U[O.sub.2]).sub.2][(P[O.sub.4]).sub.2][multiplied by]8-12[H.sub.2]O

A specimen of torbernite (#6162) labeled as coming from the Castle Dome Mountains is in the University of Arizona mineral collection. This is probably from the Castle Dome copper mine near Inspiration, where metatorbernite has been reported (Petersen, 1947).

Vanadinite [Pb.sub.5][(V[O.sub.4]).sub.3]Cl

Vanadinite is a fairly common alteration product of galena in the district, especially in solution channels and vugs where it is locally abundant. Associations include wulfenite, mimetite, cerussite, smithsonite, hydrozincite and anglesite.

William P. Blake visited Castle Dome in April of 1880 and again in the spring of 1881. He published some of his observations on vanadinite from the district in two 1881 articles, one in the Vanadinite, which occurs in considerable abundance in the claim known as the "Railroad" [= Diana mine], is a rare mineral, and has not hitherto been found in the United States, if we except some minute microscopic crystals mixed with wulfenite in the ores of the Wheatley mines, at Phoenixville, Pa.

The vanadinite [at Castle Dome] occurs in groups of hexagonal prismatic crystals with curved sides, tapering at each end, and closely resembling pyromorphite in form and grouping. These crystals are rarely over one-sixteenth of an inch in diameter ... in confused aggregations, forming crusts and filling cavities in the decomposing ores of lead, and also on fluor-spar. Some of the crystals are cavernous, presenting the appearance often seen in phosphate of lead [pyromorphite]. One side of a crust of crystals is often in distinct hexagonal crystals, and the other consists of an aggregation of minute crystals grouped in arborescent forms, and differing in color from the larger crystals. The larger crystals are generally light brown in color, with a bronzy luster. The smaller crystals are lighter, and are of various shades of orange-yellow, becoming in places nearly white with a silvery satin-like luster. The yellowish brown crystals have a wax-like appearance and luster.

Blake notes that simple chemical tests indicate a range of compositions, from vanadinite to vanadiferous mimetite.

The lustrous, green to orange vanadinite crystal groups from the Puzzler mine are among the best occurrences in the state and are very distinctive because of their color. The only similar specimens are those from the Ramsey mine.

Wilson (1933) reports vanadinite and wulfenite in vugs in the Puzzler mine. Small yellow to brown crystals have been found at the Hull mine.

The best vanadinite taken out in modern times was found in the Puzzler mine in 1988 by Mark Hay, Dick Morris and George Godas, and reported by Wilson (1989). Hundreds of attractive specimens of dull-green vanadinite clusters and crystals were recovered from a pocket on the 180-foot level. These specimens were at first assumed to be pyromorphite because of their color, but analyses provided by Chuck Lewis at Arizona State University and Dr. Terry Wallace at the University of Arizona confirmed their identity as vanadinite. Some crystals are green on one end, progressing to a reddish brown on the other end. All are simple hexagonal prisms with flat pinacoid terminations, but some crystals and clusters are distorted into a barrel-shaped habit.

Other occurrences in the Puzzler mine include the following:

40-foot level: Brown-green hoppered vanadinite crystals to 5 mm.

100-foot level: Drusy green vanadinite coating greenish yellow wulfenite crystals. Also brown to black vanadinite crystals to 5 mm; very good, blocky, greenish brown vanadinite crystals to 5 mm having good luster and, in some cases, orange termination zones; unusual hoppered gray vanadinite crystals to 5 mm; and blocky brown vanadinite crystals to 6 mm.

140-foot level: Blocky yellowish green vanadinite crystals to 6 mm.

160-foot level: Brilliant drusy brown vanadinite.

180-foot level: Brilliant orange vanadinite crystals to 3 mm; brilliant orange-brown vanadinite crystals to 3 mm on calcite; bright, greenish brown vanadinite crystals to 5 mm with calcite; curved green vanadinite crystals to 6 mm on white barite rosettes.

Willemite [Zn.sub.2]Si[O.sub.4]

Willemite has been identified on Castle Dome specimens in the collection of the Arizona-Sonora Desert Museum.

Witherite BaC[O.sub.3]

Nevius (1912) reported witherite as a constituent of the gangue in lead ores from the De Luce (= Castle Dome) mine.

Wulfenite PbMo[O.sub.4]

Wulfenite was first noted at Castle Dome by Blake (1881a). In describing vanadinite from the Railroad (Diana) claim, he remarked:

The wulfenite crystals in association are extremely brilliant and light yellow in color, presenting a beautiful appearance upon a background of green fluor-spar or white crystalline carbonate of lead [cerussite].

Wulfenite has also been found in several other mines in the Castle Dome district (Foshag, 1919). The Smithsonian Institution has specimens of wulfenite in small, blocky yellow crystals on barite and dark purple fluorite from "Howe's mine, Castle Dome district." Fine, tabular yellow crystals to over 1 cm have been found as clusters on green mimetite from the Hull mine. Blocky orange crystals to 5 mm have been found on cubical black pseudomorphs of anglesite after galena with fluorite from the same mine. In some vugs and solution channels wulfenite is found associated with hydrozincite, smithsonite, vanadinite, calcite, quartz and aragonite (Wilson, 1933). Wulfenite is also known from the Senora mine (Blake, 1881a and b) with considerable amounts of vanadinite. Greenish fluorite crystals form the matrix for wulfenite in some cases, making for attractive and unusual specimens. Fine yellow crystals to 5 mm are also known from the Danny Boy (or Dandy Boy) mine, in the Arizona-Sonora Desert Museum collection.

In the Puzzler mine, greenish yellow wulfenite crystals to 3 mm have been found on the 100-foot level, clusters of bright yellow crystals to 6 mm have been found on the 130-foot level, and very good, brilliant yellow wulfenite on blue fluorite has been found on the 180-foot level.

1880

The mineral veins of the Castle Dome District were rediscovered in the year 1863. They may truly be said to have been "re-discovered" for it is evident that the veins were opened and worked at a remote period, probably by the first Spanish padres, who made their way northward from Mexico into this country. Traces of ancient excavations on many of the veins were very plainly to be seen by prospectors in 1863, and there were, and still remain, heaps of debris consisting of the veinstone with small fragments of ore. The metal had been taken from many of the veins by these ancient miners down to a depth of from six to fifteen feet, following the vein sometimes for fifty to one hundred feet or more. The excavations appeared to have been made with long bars, and to have followed the best outcrops of metal. These old workings thus were sure guides to good metal-bearing ground a short distance below the surface. Well-worn trails leading from the mines to the banks of the Gila, only some eighteen miles distant, and the ruins there of some rude smelting furnaces, go to show that the ores mined at Castle Dome were packed on the backs of Indians to the Gila and that they were there reduced to metal, possibly being used to mix with, and to flux the more refractory but richer ores of silver from districts further east. The explorations of the veins made since 1863 have obliterated the traces of the old workings for the greater part, but they can still be seen in several places. That they are ancient is abundantly shown by the growth of the peculiar slowgrowing hard-wood trees of that region, such as the palo verde and iron wood, which were found growing in the old pits and on the piles of refuse thrown out.

New and rich silver veins had been discovered a short distance above Fort Yuma on the Colorado, which were attracting considerable attention. In the vicinity of Castle Dome, twenty-five miles from the river and thirty miles from the Fort, the veins prospected were numerous and extensive, and the ores of a very promising character. I saw some of them myself, and am satisfied they contain a great abundance of lead. No assays had been made that I heard of, but gentlemen who owned in them assured me there was silver in them as well as lead, whether much or little remained to be seen. Very little work has yet been done in the Castle Dome district, although some hundreds of claims have been prospected, and extensions run upon the most promising.

CONCLUSION

The Castle Dome district still has the potential to produce good mineral specimens in the future. It is an area which challenges the skills and energies of even the most experienced and determined field collectors, but for those willing to put in the time and labor (and risk the hazards inherent in entering abandoned mines), the ground will grudgingly yield specimens. There is still exploration work to be done, but generally only the most dangerous and least accessible workings remain unexamined. It is not a promising or safe place for inexperienced or ill-equipped collectors, or those unfamiliar with the safety precautions necessary in the desert.

ACKNOWLEDGMENTS

We would like to express our sincere appreciation to the following people for sharing their knowledge and experience of the Castle Dome district: Bob Bartsch, Richard Bideaux, Jack Crowley, Ron Gibbs, George Godas, Wayne Leicht, Peter Megaw, Bill Moller, Dick Morris, Wolfgang Mueller, Bob Pedersen, Billy Theison, Wayne Thompson, Gene Tribbey, Shirley Wetmore and Scott and Ann Williams. Kevin Franklin of the Tucson Weekly, Jeanne Broom, and the staffs at the Arizona Historical Society, the Sharlot Hall Museum and the Arizona Geological Survey kindly provided illustrations for which we are also grateful.

BIBLIOGRAPHY

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Title Annotation:includes related articles on mineral veins discovered in the Castle Dome District; old mining district
Author:Domitrovic, Anna M.; Wilson, Wendell E.; Hay, Mark
Publication:The Mineralogical Record
Article Type:Editorial
Date:Sep 1, 1998
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