Micromineralogy of Galena Ores, Burgin Mine East Tintic District Utah GEOLOGICAL SURVEY PROFESSIONAL PAPER 614-A Micromineralogy of Galena Ores, Burgin Mine East Tintic District Utah By ARTHUR S. RADTKE, CHARLES M. TAYLOR, and HAL T. MORRIS SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 614-A A study of the distribution of a variety of chemical elements in the major and minor minerals of a silver-rich lead a?id%inc replacement ore body UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 40 cents (paper cover) CONTENTS Page Mineralogy and chemistry Continued Fage Abstract_ _ ____-_______--____---___ Al Pyrite and chalcopyrite-___-_____. A9 Introduction ____________-_____--_-_. 1 Mimetite. _--____-______-_--_--. 9 Acknowledgments___ _ _______________ 1 Cerussite- _____________-_--_--_. 9 Purpose and procedure_______________ 1 Silver sulfide-___________________ 11 Mineralogy and chemistry ____________ 2 Hematite- _ _______-___-_--__--_. 11 Galena.________________________ 2 Calcite and anglesite(?)_________ 13 Polybasite- _____________________ 3 Tetrahedrite ____________________ 3 Barite and quartz___-_____---_-_- 13 Jalpaite ___-_____________--__._. 5 Element distribution._-_____-___-_-_. 13 Lead-antimony oxide or carbonate. 8 Summary and conclusions._______._. 16 Sphalerite. _ _ ___-_-___--______. 8 References cited-____________________ 17 ILLUSTRATIONS [All Illustrations are photomicrographs] FIGURE 1. Chainlike series of polybasite and tetrahedrite inclusions in galena._____________________________________ A4 2. Large grain of tetrahedrite locked in fine-grained galena._______________________________________________ 5 3. Granular intergrowth of jalpaite and galena surrounded and replaced by cerussite.______-__--___-________. 5 4. Mimetite forming along a microfracture in galena.___________________________________________________ 6 5. Replacement of remnant grains of sphalerite, quartz, and barite by galena,_______________________________ 8 6. Veinlet of late(?) barite containing fragments of pyrite, chalcopyrite, sphalerite, and galena cutting across quartz. 9 7. Mimetite along contact between galena and barite gangue______________________________________________ 10 8. Alteration of galena to cerussite localized along cleavage planes________________-_______-_---_-_-________- 11 9. Fine-grained secondary silver sulfide dispersed in secondary cerussite.-_________-___--__-_-_-___-___-__-_- 12 10. Replacement of remnant quartz and segmented barite by galena, which was subsequently altered to cerussite- _ _ 13 11. Alteration of galena to cerussite.____________________________________________________________________ 14 TABLES TABLE 1. Minerals in the galena ores of the Burgin mine._________________ A2 2. Chemical and spectrographic analyses of galena ores, Burgin mine. 3 3-7. Analyses of 3. Polybasite-__________________________________________ 3 4. Tetrahedrite-________________________________________ 3 5. Jalpaite__--_-_-_____-______-__-_-____-_____________ 5 6. Sphalerite_-_-_-_--__-__--______--__-__-___________. 8 7. Mimetite__________________________________________ 9 in SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY MICROMINERALOGY OF GALENA ORES, BURGIN MINE, EAST TINTIC DISTRICT, UTAH By ARTHUR S. KADTKE, CHARLES M. TAYLOR, and HAL T. MORRIS ABSTRACT sentative of two major varieties of lead ore in the cen­ Analyses of argentiferous galena ores from the Burgin mine, tral part of the main Burgin ore body. Samples of both Utah, by electron microprobe, emission spectograph, and wet were collected by H.T. Morris in November 1965 from chemical method indicate distinctly different amounts of silver the 1,200-foot level of the mine shortly after the main in two general types of galena. Massive coarse-grained galena ore body was first reached on this level. Type 1 ora is contains an average 0.22 percent silver by weight (approxi­ mately 64 ounces per ton), whereas fine-grained galena has less massive coarse-grained galena which forms a lead-rich than 0.04 weight-percent silver (approximately 12 ounces per zone near the f ootwall of the deposit. Type 2 ore is some­ ton). The primary silver minerals dispersed in the galenas in­ what finer grained galena that is intergrown with minor clude polybasite, tetrahedrite, and jalpaite. Secondary silver sphalerite near the hanging wall of the deposit. T^he sulfides, including argentite (or acanthite) and jalpaite, are contact between the two types of galena ore is abrupt concentrated in cerussite along fractures. and apparently indicates.either a change in the compo­ INTRODUCTION sition of the ore solutions during deposition or postdepo- The Burgin mine, in the East Tintic mining district, sitional leaching and recrystallization of part of the ore Utah, has recently become a major source of lead, zinc, body. ACKNOWLEDGMENTS and silver ores in an area that is widely known for rich and extensive replacement deposits (Lovering and The writers thank Mr. Gale Hansen, former mine su­ Morris, 1960, p. 1116-1147; Bush and Cook, 1960, perintendent, and Mr. William M. Shepard, mine geolo­ p. 1507-1540). The principal ore body in the mine, from gist, for permission to sample the ore body of the Bur- which the samples described in this report were taken, gin mine. Dr. Victor Macres, President, Materials is localized in sheared and brecciated rocks near the Analysis Co., generously permitted the use of Model sole of the East Tintic thrust fault. This ore body is 400 electron-beam microprobe analyzers and other facili­ reported to contain more than 1,250,000 tons of ore with ties at the company laboratories in Palo Alto, Calif. an average content of 10 ounces of silver per ton, 15 PURPOSE AND PROCEDURE percent lead, and 12 percent zinc (Mining Congress Journal, 1961). Several times this amount of lower Examination of the galena ores from the Burgin mine grade ore forms a casing around the high-grade ore was undertaken to (1) study the distribution of silver, body, and other ore bodies, estimated to contain an even (2) identify all ore and gangue minerals, (3) study tex- larger quantity of medium- and low-grade ore, have tural and physical relationships of the minerals, p,nd been discovered nearby. In general, the ores consist of (4) study chemistry and element distribution of the various proportions of argentiferous galena, sphalerite, minerals. pyrite, and minor quantities of other metallic minerals Mineral identifications were made by using the com­ in a gangue of rhodochrosite and baritic jasperoid. bined techniques of electron microprobe analysis, X- These minerals replace brecciated masses of Cambrian ray powder diffraction, and microscopy. The extremely limestone that have been overturned and thrust over small grain size of many of the phases necessitated ex­ argillaceous limestones of Ordovician age. All the Pale­ tensive use of the electron microprobe analyzer. Sample ozoic rocks in the mine area are concealed beneath al­ preparation wais done by Radtke and Taylor in the tered quartz latite lavas of Eocene age that postdate the laboratories of the Materials Analysis Co., Palo Alto, structural events but predate ore deposition. Calif., and the U.S. Geological Survey, Menlo Park, The two ore types described in this report are repre­ Calif. All analytical work was done with Materials Al A2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Analysis Co. Model 400 two-channel and three-channel tion corrections by Philibert (1963), and the Dmcumb electron-beam microprobe analyzers. and Shields' (1966) overvoltage correction. Mineral textures and physical relationships were MINERALOGY AND CHEMISTRY studied in polished section and, to a lesser extent, in hand specimen and are shown in numerous photomicro­ The first of the two types of ore, designate:! ''type graphs. The polished sections were made by mounting 1," is coarsely crystalline galena with thin coatings of thin wafers of ore in epoxy casting resin set in stainless secondary minerals. The second, designated "type 2," steel rings. The surfaces selected for study were ground, is massive fine-grained crystalline galena with minor impregnated, and polished following the method de­ amounts of sphalerite and abundant overgrowths of scribed by Taylor and Kadtke (1965). Use of the stain­ secondary minerals. less steel mounting ring and careful sample prepara­ All minerals identified in the ore samples ar°> listed tion resulted in virtually no loss or plucking of galena with their compositions in table 1. and other minerals from the surface, as well as in ex­ TABLE 1. Minerals in the galena ores of the Bur gin mine tremely low relief between galena and quartz. Bulk samples of the galena ores were analyzed by .___.. PbS Sphalerite_ ______ ZnS standard wet-chemical and spectrographic techniques. .__... FeS2 The chemical compositions of all minerals were deter­ Chalcopyrite_ _ _ _ _ .______ CuFeS, mined with the electron microprobe analyzer. Certain Tetrahedrite- _____._._-_ (Cu, Zn, Ag) 12 (Sb, As) 4 S» aspects studied in detail include chemical zoning within Polybasite- _____________ (Ag, Cu) 16 Sb2 Sn minerals and element-concentration gradients across Jalpaite. _______________ CU0 .46 Agj.54 S Silver sulfide* ------ Ag2S mineral boundaries. Numerous electron-beam scanning Lead-antimony (EBS) X-ray images illustrate