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THE SHIRLEY ANN CLAIM, INYO COUNTY, CALIFORNIA.

The Shirley Ann lead-copper deposit, recently incorporated into the new Death Valley National Park, has produced a suite of well-formed oxidation-zone minerals including a new species:ferrisurite.

INTRODUCTION

While a graduate student in geology at the University of Southern California in the late 1970's, I supplemented my studies with personal mineral collecting trips. In a California Division of Mines report (McAllister, 1955), I came across a reference to wulfenite and cerussite at the Shirley Ann claim, a small oxidized lead-copper deposit near the north end of the Panamint Range, just west of Death Valley National Monument. As everyone knows, it is difficult to find localities with collectable minerals that have not already been over-collected. I had never seen or heard of specimens from this locality, and it certainly seemed remote and obscure enough to have escaped collector notice. I decided that this would be a suitable destination. However, after suffering a variety of scrapes and dents to my car and finally punching a hole in the gas tank, I concluded that my 1975 Plymouth Valiant was not a suitable field vehicle. The Shirley Ann claim would have to wait until this poor student could afford better wheel s.

Ten years later, I purchased a four-wheel drive truck, and my mineral collecting trips resumed. While on a collecting trip in the vicinity of the Shirley Ann claim I decided to pay the site a visit. The claim supposedly could be reached via a 3 to 4-km foot trail shown on the topographic map, but considering the very rugged nature of the terrain and the age of the trail, I decided that locating and following the trail would be difficult. After further consideration, I concluded that by following the dry washes I would end up only a short distance from the claim.

The presumably easier course proved to be far from easy. The several kilometer-long hike traversed some nearly impenetrable grapevine jungles growing near springs. Then, the canyon became very narrow and a boulder fall made it impassable. The boulders were too large (the size of cars) to climb over and too tightly packed to crawl between. Sitting there somewhat dejectedly, I consoled myself that I had made a valiant effort. Before starting back, I lingered a bit, staring at the steep canyon walls, when I sensed something unnatural about the rock formations. Someone had built a crude set of switchbacks up and around the boulder fall! The constructed trail led me past this and additional obstacles until, before long, I easily located the claim.

The crystallized minerals that I found on the dumps included wulfenite and mimetite, but they were all of micromount size and not particularly abundant. At the time it didn't seem that my considerable efforts had been adequately rewarded; however, among the material I carried back was a single specimen containing a 3mm vug with a spray of an unusual, fibrous, olive-brown mineral. An X-ray diffraction (XRD) pattern of the fibrous mineral closely matched that of surite, a silicate related to the smectite group. A qualitative chemical analysis confirmed all of the essential elements in surite, except aluminum, and also indicated the presence of iron. This suggested that the unknown might be an iron analog of surite.

Between the time that the XRD pattern was obtained and the identification was made, the original and only specimen was lost! This prompted a hasty return trip to the Shirley Ann claim and, at that time, I found sufficient material to permit formal description of the new mineral ferrisurite (Kampf et al., 1992). Besides ferrisurite, the second visit yielded well-formed microcrystals of wulfenite, cerussite, mimetite, linarite and malachite.

LOCATION

The Shirley Ann claim (elevation 1400 meters) is located about 300 meters southwest of Big Dodd Spring in the Ubehebe mining district, which is about 45 km due east of Lone Pine and 22 km north of Darwin, in Inyo County, California. The claim can only be reached by hiking approximately 4.3 km from the Saline Valley road or 8.5 km from the Lippencot mine.

In 1996 the area surrounding the Shirley Ann claim was incorporated into the newly established Death Valley National Park, and for this reason, mineral collecting is now forbidden there. As a result of the nearby springs, this area has an abundance of interesting wildlife. The juxtaposition of the springs on the desert environment makes this one of very few places in the desert where one can find grapevine jungles and cat tails in close proximity with cacti. During early collecting trips it was not uncommon to encounter a herd of bighorn sheep and, on one occasion while at the claim, a large ram appeared and vocally protested the presence of an intruder in its territory.

HISTORY

It has been conjectured (McAllister, 1955) that the Shirley Ann claim had been worked as early as 1902 under the name of the Eureka claim, based on limited physical descriptions given in early mining records and mineral reports. Inyo County records indicate that the Shirley Ann claim was located by Earle Carr, Jr. in 1940, and by 1950 it was owned by H. P. Gower. At that time the workings consisted of a 35-meter-long southwest-trending adit with two short adits north and south of the main portal (Fig. 2). About halfway into the main adit a steeply inclined shaft reaches 12 meters to the surface, where it connects with a short (8 meter) adit. In the lower main adit a short drift extends about 8 meters southwestward from the shaft. The southwest extension of veins exposed in the adits are explored by a series of surface trenches that extend for about 80 meters. There is no significant difference in the description of the workings given by McAllister (1955) and the present-day workings, indicating that very little work has been done since that time, probably because of the difficult access.

GEOLOGY

The Shirley Ann claim is situated along the eastern margin of a metamorphosed block of Paleozoic limestone (Pogonip Formation?) that is in contact with a calcic facies of the Cretaceous Hunter Mountain quartz monzonite, that ranges in composition from pyroxene-biotite gabbro to olivine gabbro. The mineral deposits of the Shirley Ann claim were probably controlled by faults in the metamorphosed sedimentary rocks (shaly and silty limestones) (McAllister, 1955). The principal area of mineralization, which contains lead and copper ores, is concentrated along the main adit and extends up the shaft to the connecting small adit. Galena altering to cerussite occurs as veins in calcite and quartz gangue in the lower adit and massive cerussite is common on the dumps. Covellite occurs as rims on partially altered galena and along cleavage faces therein. Minor wulfenite, mimetite, pyrite, chalcocite, chalcopyrite, hematite, chrysocolla, and malachite occur locally, often associated with altered galena veins. In the sout hwest-trending surface trenches the quartz and calcite veins locally contain minor amounts of chrysocolla and crystallized malachite, galena, cerussite, wulfenite and linarite. The Shirley Ann claim differs from the lead deposits at the larger mines in the area in that there is a greater abundance of copper minerals and fewer zinc minerals. Ferrisurite was discovered in calcite and quartz gangue on the dumps, where it is commonly associated with cerussite, galena, wulfenite and mimetite,

MINERALS

The species listed below are those that are most likely to be found as well crystallized microminerals and therefore are more likely to be of interest to collectors. The majority of mineral identifications have been made by X-ray diffraction (XRD) and/or energy dispersive X-ray spectroscopy (EDXS) using a scanning electron microscope (SEM). All figured specimens are in the collection of, and were photographed by, the author (except where noted).

Cerussite [PbCO.sub.3]

Cream to gray, massive cerussite, which formed from the alteration of galena, is common on the dumps and in the underground workings. Minute crystals ([less than]1 mm) tend to be colorless and transparent, while larger (3-4 mm) crystals, which are relatively uncommon, are usually translucent gray. Equant cyclic twins to 4 mm have been found associated with galena bodies in the lower adit. In a surface trench above the upper adit, V-shaped twinned cerussite crystals (to 4 mm) are found associated with milky quartz crystals and malachite. These crystals are typically covered with a thin coating of black plattnerite, but lustrous, unaltered bladed crystals have also been observed.

Duftite PbCu([AsO.sub.4])(OH)

Small clusters (0.3 mm) of dark red-brown duftite, consisting of minute (0.01 x 0.07 mm) blades, were observed with wulfenite on small milky quartz crystals from a specimen collected in one of the upper trenches.

Ferrisurite [(Pb,Ca).sub.2-3][([CO.sub.3]).sub.1.5-2][(OH,F).sub.0.5-1]-[[(Fe,Al) .sub.2][(Si,Al).sub.4][O.sub.10][(OH).sub.2]]*[nH.sub.2]O

Ferrisurite is the ferric iron analog of surite. Surite, which has aluminum in place of iron, was first described as compact aggregates in the oxidation zone of lead-zinc-copper deposits at the Crus del Sur mine in Argentina (Hayase et al., 1978). Additional data on surite have been published by Uehara et al. (1997).

The following chemical, structural and physical properties of ferrisurite are summarized from Kampf et a!. (1992). Ferrisurite crystallizes in the monoclinic system and has pseudo-orthorhombic symmetry ([beta] [approximate] 90[degrees]). The X-ray powder diffraction patterns of ferrisurite and surite are very similar. The structure of ferrisurite! surite probably consists of cerussite-hydrocerussite layers, represented by the first portion of the above formula, interspersed between smectite layers (second part of formula). Ferrisurite crystals are transparent to translucent with pale yellow-green color and greenish yellow streak. Compact radial aggregates have a medium to dark forest-green color and olive-green streak. Crystals are flattened on (010) and elongate parallel to [100]. The maximum crystal dimensions are 3 mm along [100], 0.01 mm along [010] and 0.04 mm along [001]. Twinning has not been observed. Ferrisurite exhibits silky luster, has perfect {010} cleavage and a Mohs' hardness of approximately 2-2.5 . It effervesces in cold 1:1 HCl and leaves a gelatinous residue. Ferrisurite is optically biaxial (+) with refractive indices, measured in white light, of: a = 1.757, b = 1.763, c = 1.773. The optical orientation is X = c, Y = b, Z = a, and the mineral is pleochroic with X = yellow, Y = brown, and Z = light green. No fluorescence under longwave or shortwave ultraviolet radiation has been observed.

Ferrisurite occurs in three main habits, some of which were not known at the time of its formal description. The first consists of 2-3 mm fibrous olive-green to golden brown aggregates which are found in small, 3-5 mm cavities in coarse-grained brown calcite and fine-grained white to gray quartz gangue. Such aggregates in vugs served as the type specimens for the formal description of ferrisurite. Free-standing, undamaged, radiating fibrous groups (to 3 mm) are exceedingly rare. More typically the ferrisurite crystals are bent or matted. Closely associated minerals include mimetite, calcite and wulfenite, which may or may not be closely associated with altered galena. Occasionally, radiating groups of ferrisurite occur in bunches up to 1.5 cm. In the second habit, ferrisurite forms olive-brown to dark green radiating fibrous aggregates (to 4 mm) on fracture planes along thin (1 mm) veins in quartz gangue. Fracture surfaces up to 6 x 9 cm covered with radiating ferrisurite have been observed, but are very unc ommon. Ferrisurite of the third habit consists of compact olive-green to dark green fibrous aggregates intimately intergrown with coarse-grained quartz and minor, massive, gray cerussite, chrysocolla, mimetite and galena. This material is more disseminated and difficult to isolate from its surroundings.

Occasionally white to cream colored pseudomorphs of a smectite mineral faithfully retain the ferrisurite radiating fibrous morphology. This is not unexpected because it has been shown that surite reacts with acids to produce smectite as a result of dissolution of the interlayer Pb-Ca carbonate (Hayase et al., 1978). More commonly, alterations of ferrisurite are yellowish to brownish in color and less of the radiating fibrous structure is retained.

Fornacite [(Pb,Cu).sub.3][[(Cr,As)[O.sub.4]].sub.2](OH)

Minute (0.25 mm) blades of olive-green fornacite were confirmed on one specimen collected from the dumps.

Galena PbS

Clots and stringers of primary galena up to 10 cm in size are found in some of the underground workings and are surrounded by cerussite and chrysocolla. Thin films of covellite have been observed on some galena cleavages and as thin rims on altered galena clots.

Linarite PbCu([SO.sub.4])[(OH).sub.2]

Bright blue films of linarite (to 4 x 6 cm) have been observed with malachite on the dumps by the upper adit; 1-2 mm crystals on milky quartz crystals have been collected from one of the surface trenches above the upper adit. Associated minerals include malachite, cerussite, galena and chrysocolla.

Malachite [Cu.sub.2]([CO.sub.3])[(OH).sub.2]

In one of the surface trenches above the upper adit, 3-4 mm pale green radiating tufts of malachite are found with cerussite, linarite, chrysocolla and galena in milky quartz veins. At the same site, small (1-mm), transparent, dark green flat plates and bladed crystals have also been observed.

Mimetite [Pb.sub.5][([AsO.sub.4]).sub.3]C1

Mimetite is relatively common and displays a wide range of morphologies and colors. Most often it is found as small (to 0.5 mm) white to pale yellow rice-shaped aggregates, which occur with ferrisurite and wulfenite. Less commonly it is found as yellow hexagonal prisms (to 1 mm) and pale gray radial aggregates (to 2 mm) in calcite gangue. Pale gray-green spherical masses (to 6 mm) have also been found in small vugs lined with milky quartz crystals associated with an altered galena body in the lower adit. Acicular, pale orange crystals occur with wulfenite, and matted aggregates of very fine acicular yellow crystals have also been found on milky quartz crystals.

Wulfenite [PbMoO.sub.4]

Wulfenite, while never abundant or very large, is one of the most interesting minerals from the Shirley Ann claim because of the multitude of crystal habits that have been collected. It has been found both in the lower adits and in quartz veins in the upper trenches. Thin tabular crystals to 3 mm occur as solitary individuals in small vugs associated with altered galena bodies. These crystals may be transparent, show signs of phantoms, and range in color from pale yellow to medium or dark orange. Gray nodular or orange semi-acicular mimetite is commonly associated. As crystals become more equant the pyramid faces become more prominent; groups of individual crystals to 2 mm with this mixed morphology have been found coating fracture planes in the rock. The pyramid faces can also become developed to the point where the pinacoid is absent and the crystals are relatively elongated. Homo-epitactic pyramidal overgrowths on tabular crystals have also been observed.

Pale gray tabular crystals (to 1.5 mm) that were suspected of being wulfenite were found to contain appreciable tungsten, in addition to lead and molybdenum. The exact composition was not determined but semi-quantitative analysis indicate that tungsten may be substituting for up to 20% of the molybdenum in these wulfenites. Associated minerals include gray mimetite, orange wulfenite of various habits and cerussite. Gray-blue chrysocolla overgrowths on these tungstenian wulfenites have also been observed.

ACKNOWLEDGMENTS

The author would like to thank A. R. Kampf, L. L. Jackson, G. B. Sidder and E. E. Foord for describing ferrisurite. A. R. Kampf also reviewed this manuscript and provided helpful suggestions. G. W. Stupian provided the SEM photographs of ferrisurite.

REFERENCES

HAYASE, K., DRISTAS, J. A., TSUTSUMI, S., OTSUKA, R., TANABE, S., SUDO, T., and NISHIYAMA, T. (1978) Surite, a new Pb-rich layer silicate mineral. American Mineralogist, 63, 1175-1181.

KAMPF, A. R., JACKSON, L. L., SIDDER, G. B., FOORD, E. E., and ADAMS, P. M. (1992) Ferrisurite, the [Fe.sup.3+] analogue of surite, from Inyo County, California. American Mineralogist, 77, 1107-1111.

McALLISTER, J. F. (1955) Geology of mineral deposits in the Ubehebe Peak quadrangle, Inyo County, California. California Division of Mines Special Report

McALLISTER, J. F. (1956) Geology of the Ubehebe Peak quadrangle, California. U.S. Geological Survey GQ-95.

UEHARA, M., YAMAZAKI, A., and TSUTSUMI, S. (1997) Surite: Its structure and properties. American Mineralogist, 82, 416-422.
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Author:Adams, Paul M.
Publication:The Mineralogical Record
Geographic Code:1U9CA
Date:Sep 1, 2001
Words:2721
Previous Article:THE VAL GRAVEGLIA MANGANESE DISTRICT, LIGURIA, ITALY.
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