DEPARTMENT OF THE INTERIOR FRANKLIN K. LANE, Secretary / ? */ 2~ J o UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, Director Bulletin 681 THE OXIDIZED ZINC ORES OF LEADVILLE COLORADO BY G. F. LOUGHLIN WASHINGTON GOVERNMENT PRINTING OFFICE 1918 *? o o CONTENTS. Page- Introduction. ............................................................. 7 Discovery.....................................................'............ 7 Early accounts of zinc carbonate and silicate............................. 8 Recent discovery of oxidized zinc ore bodies............................. 12 Production................................................................ 13 Literature.................................................................. 16 Mineralogy................................................................... 17 Zinc-ore minerals....................................................... 17 Smithsonite....................................................... 17 Hydrozincite....................................................... 18 Aurichalcite..................................'..................... 19 Calamine......................................................... 20 Hetaerolite....................................................... 21 Chalcophanite..................................................... 24 Zinciferous clay................................................... 24 Deschenite........................................................ 28 Associated minerals.................................................... 28 Iron oxides........................................................ 28 1 Manganese oxides.................................................. 29 Dolomite.......................................................... 29 Manganosiderite............... 1................................... 29 Calcite........................................................... 30 Aragonite and nicholsonite.......................................... 30 Barite.,........................................................... 31 Plumbojarosite..................................................... 31 Opal, chalcedony, and quartz....................................... 32 Sericite........................................................... 33 Kaolin............................................................ 33 Sulphides.......................................................... 33 Native silver...................................................... 34 Paragenesis........................................................... 34 Varieties of ore........................................................'..... 36 Gray carbonate ore.................................................... 36 Occurrence....................................................... 36 Megascopic features:.............................................. 36 Microscopic features............................................... 37 Chemical composition............................................. 39 Brown carbonate ores................................................... 40 Megascopic features................................................ 40 Microscopic features................................................ 42 Chemical composition............................................. 44 4 CONTENTS. Varieties of ore Continued. Page. Black zinc ore........................................................ 46 White or "talcy " zinc ore.............................................. 47 Analyses............................................................... 47 Range in metal content of the ores........................................... 48 Zinc content.......................................................... 48 Other contents......................................................... 50 Distribution and mode of occurrence of the ores............................. 51 Geographic distribution................................................ 51 Distribution with respect to kinds of country rock....................... 51 Relations to the different kinds of lead carbonate and mixed sulphide ore bodies.............................................................. 51 Shapes and sizes of ore bodies........................................... 54 General features.................................................... 54 Carbonate Hill ore bodies.......................................... 57 Character of boundaries of the ore bodies................................. 61 Relations to oxidized iron and manganiferous iron ores .................. 64 Vertical distribution and relation to depths of oxidation and ground-water level................................................................ 64 Lack of association with secondary sulphides............................. 66 Genesis.................................................................... 68 First stage............................................................ 69 Derivation of materials............................................... 69 Deposition of materials from solution................................ 72 Second stage.......................................................... 80 Third stage............................................................ 81 Summary.............................................................. 83 Prospecting for bodies of oxidized zinc ore................................... 85 Index................................................................... 89 ILLUSTRATIONS. Page. PLATE I. A, Gray zinc carbonate ore; B, Chalcophanite and calamine coating brown zinc carbonate ore...................................... 18 II. A, Photomicrograph of gray zinc carbonate ore inclosing remnants of sulphide ore; B, Photomicrograph of zinc carbonate replacing manganosiderite............................................... 19 III. A, Brown zinc carbonate ore with fine druses of smithsonite; B, Photomicrograph of specimen shown in A ....................... 20 IV. A, Brown zinc carbonate ore with druses of calamine; B, Calamine druse coating brown zinc carbonate ore......................... 21 V. A, Brown zinc carbonate ore with druses of aurichalcite; B, Photo- micrograph showing aurichalcite and calamine filling cavity in brown zinc carbonate ore; C, Photomicrograph of vein of calamine, aurichalcite, and opaline silica in low-grade brown zinc ore...... 24 VI. A, White zinciferous clay; B, Brown dense zinciferous clay; C, Brown banded zinciferous clay; D, E, Aragonite filling cavities in brown iron oxide.............................................. 25 . VII. Plan of zinc carbonate ore bodies in workings of Western Mining Co., Carbonate Hill................................................. 58 VIII. Sections through ore bodies shown in Plate VII.................... 60 FIGURE 1. Diagram showing percentages of constituents in zinciferous clays, arranged in order of increasing alumina......................... 27 2. Diagram showing distribution of calamine along bedding planes and cross fractures in brown zinc carbonate ores............. %.. 42 3. Plan and sections of lead-silver stopes in Belgian mine............ 53 4. Diagrams illustrating relations of oxidized zinc ore bodies to lead carbonate stopes in the Oro La Plata mine..................... 54 5. Plan and sections showing relation of oxidized zinc ore body on the Dome claim to old lead carbonate stope..................... 55 6. Plan and section showing relations of oxidized zinc ore stopes to old lead carbonate stopes, Tucson mine........................ 56 7. Plan and section showing relations of oxidized zinc ore to old lead carbonate stopes in Chrysolite mine........................... 57 5 THE OXIDIZED ZINC ORES OF LEADVILLE, COLORADO. By G. F. LOUGHLIN. INTRODUCTION. Oxidized zinc ores were first exploited in the Leadville mining district, Colorado, after the Geological Survey's field study of the other ores had been completed. In the summer of 1913 the writer was detailed to study these ores and spent four weeks in the district dur­ ing July and August. The present report was completed early in 1914 and transmitted to form a chapter in a monogpaph on the geology and ore deposits of the district, but owing to continued delay in the completion of the monograph it has been decided to publish this chapter in advance. The mine operators and engineers in the district gave the writer till possible assistance in his work. Thanks are especially due to Messrs. Nicholson, MacDonald, and Dalrymple, of the Western Min­ ing Co.; Messrs. Platt and Kleff, mine surveyors and lessees of the New Dome property; Messrs. Davis and Pendery, of the Yak Co.; Messrs. Argall and Aicher, of the Iron Silver Co.; the officers of the Ibex Co.; Mr. Warren F. Page, of the Luema Mining Co.; and Mr. John E. Curley, State inspector of mines. To the several other lessees, foremen, and miners who rendered assistance at different times the writer here expresses his hearty thanks. Thanks are also due to Mr. E. C. Wells, of the United States Geological Survey, for criticism of the discussion of chemical processes involved in the deposition of the oxidized zinc ores. DISCOVERY. After it was realized, in 1910, that large deposits -of oxidized zinc ores were present in the Leadville district, considerable discussion arose over the fact that these ores had been so long overlooked both by the mining engineers and geologists who had made frequent visits to the mines and by the mine officers and assayers who had been working in the ore and handling samples of it for several years. It 7 8 OXIDIZED ZINC OKES OF LEADVILLE, COLO. must be admitted that the ore had been exposed