ILLUSTRATIONS. Pa PLATE I. Geologic map of the southern parts of the Caddo Gap and De Queen II. Pike gravel member at Bluff Ford on Muddy Fork, 1 mile west of III. Pebbles from the Bingen formation. IV. Map showing phosphate reserves in Utah July 1, 1917...... V. Map showing the distribution of phosphate deposits along the north and south slopes of the Uinta Mountains, northeastern Utah.. In pocke FIGURE 1. Sketch showing relation of lamellae of smithsonite to open part of a fracture.... 2. Diagrammatic sketch showing relations of curved lamellae to two 3. Simplified sketch of a specimen of smithsonite showing extreme 19 6. Generalized section of Cretaceous rocks exposed in the Caddo Gap 7. Index map showing the location of the phosphate field in the Uinta 9. Sketch plan showing relations of the principal claim groups in the 98 10. Diagram showing relative position of rock zones in the Phoenix 66 11. Cross section of a part of the Rico lode, in the Phoenix Mountains IV 99 103 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1918. PART I. METALS AND NONMETALS EXCEPT FUELS. F. L. RANSOME, E. F. BURCHARD, and H. S. GALE, Geologists in charge. INTRODUCTION. The Survey's "Contributions to economic geology" have been published annually since 1902. In 1906 the increase in the number of papers coming under this classification made it necessary to divide the contributions into two parts, one including papers on metals and nonmetals except fuels and the other including papers on mineral fuels. In 1915 the year included in the title was changed from the year in which the field work reported in these papers was done to year of publication, and in consequence there was no volume entitled "Contributions to economic geology, 1914." The subjoined table gives a summary of these bulletins. the United States Geological Survey "Contributions to economic geology.” The date given is that of the complete volume; beginning with Bulletin 285, the papers have been issued as advance chapters as soon as they were ready. As the subtitle indicates, the papers included in these volumes are of two classes (1) short papers giving comparatively detailed descriptions of occurrences that have economic interest but are not of sufficient importance to warrant a more extended description; (2) preliminary reports on economic investigations the results of which are to be published later in more detailed form. These papers are such only as have a direct economic bearing, all topics of purely scientific interest being excluded. Brief abstracts of the publications of the year are given in the annual report of the Director. The complete list of Survey publications affords, by means of finding lists of subjects and of authors, further aid in ascertaining the extent of the Survey's work in economic geology. The reports on work in Alaska have been printed in a separate series since 1904, the volumes so far issued being Bulletins 259, 284, 314, 345, 379, 442, 480, 520, 542, 592, 622, 642, and 662. ZINC CARBONATE AND RELATED COPPER CARBONATE ORES AT OPHIR, UTAH. By G. F. LOUGHLIN. INTRODUCTION. Although the Ophir mining district, Utah, has long been an important source of lead carbonate and of lead and zinc sulphide ores, zine carbonate ore was not shipped from it until 1913. On July 23, 1914, the writer visited the two mines, the Cliff and Hidden Treasure, that were shipping zinc carbonate ore. The output of this ore from each mine was small, but the deposits presented some very interesting features, the principal of which were the marked lamellar structure of the zinc carbonate in contrast to that in other deposits studied by the writer,1 the prevailing absence of calamine, and the intimate association of the zinc carbonate with copper carbonates. The present paper is devoted mainly to these features and is offered as a further contribution to the literature on the genesis of oxidized zine ores. METAL CONTENT. As oxidized zinc ore has been shipped from only two mines no figures showing the quantity and value are presented here, as this might disclose individual returns given in confidence. It is probable that these ores yielded only a minor fraction of the total quantity of zine from the district during 1913 and later years. mine may per cent Some idea of the metal content of the ore from the Hidden Treasure be obtained from the following data on carload shipments, supplied by Mr. Keith, of the Empire Zinc Co., through C. W. Henderson, United States Geological Survey: 36.09 per cent zinc and 2.3 per cent lead; 40.2 per cent zinc and 1.5 per cent lead; 35.84 zinc, about 1 per cent copper, 0.75 ounce to the ton of silver, and no lead or gold. The ore, as a rule, is said to contain no gold, 1 ounce to the ton of silver, and 1 per cent each of lead and copper. In view of the relation of copper to zinc described on page 10, the low content of copper is noteworthy and indicates careful sorting of the ore. No 'Loughlin, G. F., The oxidized zinc ores of the Tintic district, Utah: Econ. Geology, vol. 9, pp. 1-19, 1914; The oxidized zinc ores of Leadville, Colo. : U. S. Geol. Survey Bull. 681, 1918. determinations of copper, lead, silver, or gold were made on the oxidized zinc ore from the Cliff mine. At the time of visit, in 1914, ore containing less than 35 per cent zinc could not be shipped at a profit. OCCURRENCE. Both of the deposits studied lie at shallow depth and close by the summit of the ridge and are typically associated with lead deposits. The wall rock is rather coarse grained bluish-gray limestone, probably of Mississippian age, cut by numerous vertical veinlets of calcite, 1 to 3 inches thick, which are genetically associated with the original sulphide ore of the district. The lead ore bodies are in part of pipelike form along fissures and in part deposits formed by replacement along the bedding. They consist of galena, partly oxidized to cerusite and minor oxidation minerals. Their lower parts are incased by shoots of oxidized zinc and copper ore. As in other lead-zinc districts, the material in some of these shoots was formerly regarded as waste and used to fill up old lead stopes, but in 1913 and 1914 its value was recognized, and it was sorted into zinc and copper ores and shipped along with newly broken ore obtained around recently mined lead stopes. The zinc and copper carbonate minerals in these ores as seen in ore piles were intimately associated, and the two kinds of ore graded into each other. The writer was informed that occasionally pieces of ore were broken in two and one part thrown on the pile of copper ore and the other on that of zinc ore. Observations made underground and at the ore piles indicated that the zinc carbonate ore was deposited by replacement of limestone prior to the deposition of the copper carbonates and was later in part replaced by the copper carbonates. Mr. D. W. Lynch, lessee at the Hidden Treasure mine in 1914, stated that zinc and copper ores in a part of the mine which the writer could not visit lay along the footwall of an old bedded lead stope; that copper carbonates lay nearest to the lead stope and graded downward, both along and normal to the dip of the wall rock, into zinc carbonate. These statements accord with evidence gained by paragenetic study of material in the ore piles. MINERALOGY, The principal ore minerals present are ferruginous smithsonite, aurichalcite, malachite, and azurite. Calamine, hydrozincite (?), and a zinc-bearing clay have been noted in very small quantity on a few specimens. A little cuprite was seen in the copper ore but not in association with zinc minerals, and one specimen showed remnants of chalcopyrite. The principal minerals associated with the ore are limonite and psilomelane or wad. Calcite and quartz are present in small quantity. |