According to H. T. Morris (in Cook, 1957, p. 4-26), the East Tintic Mountains are composed of a section of sedimentary rocks more than 32,000 feet thick, which are complexly faulted and folded, intruded by quartz monzonite and monzonite stocks, plugs, and dikes, and covered by quartz latite and latite flows and pyroclastics. The oldest rocks are late Precambrian in age and are phyllitic shales and quartzites tentatively correlated with the Big Cottonwood Formation of the Wasatch Range. Rocks of Cambrian age are the Tintic Quartzite and the super jacent carbonate and shale formations consisting of the Ophir Formation, Teutonic Limestone, Dagmar Limestone, Herkimer Limestone, Bluebird Dolomite, Cole Canyon Dolomite, Opex Formation, and Ajax Limestone. The carbonate lithology is persistent throughout the remainder of the Paleozoic section, which consists of the following formations: Opohonga Limestone and Fish Haven Dolomite of Ordovician age, the Bluebell Dolomite of Late Ordovician, Silurian, and Devonian age, the Victoria Formation of Devonian age, the Pinyon Peak Limestone of Late Devonian and Mississippian (?) age, the Madison Limestone, Deseret Limestone, Humbug Formation, and Great Blue Limestone of Mississippian age, the Manning Canyon Shale of Mississippian and Pennsylvanian age, the Oquirrh Formation of Pennsylvanian age, and the Diamond Creek (?) Sandstone and Park City(?) Formation of Permian age.
This entire sedimentary section was folded into a series of north-trending anticlines and synclines, the most prominent of which are, from west to east, the North Tintic anticline, the Tintic syncline, and the East Tintic anticline. The rocks were also complexly faulted several times and were intruded by quartz monzonite and monzonite porphyry stocks and latite, andesite, and diabase plugs, dikes, and sills. Tertiary extrusive rocks, consisting of the Packard and Fernow Quartz Latites and younger latite and basalt, cover large areas in the southern and eastern part of the East Tintic Mountains (H. T. Morris, in Cook, 1957, p. 30-51).
The ore deposits occur in limestone replacement bodies and in fissure veins, which have a spatial relationship with each other and with the intrusive rocks. Many of the replacement bodies, which were by far the most productive deposits in the district, are on the northward projection of fissure veins. Four principal replacement ore zones are recognized - the Gemini, Chief, Godiva, and Iron Blossom. They are elongate bodies, continuous in strike but discontinuous vertically, occupying a strati-graphic interval of 6,000 feet. The ore zones are continuous across faults; at certain fault intersections, chimneys of ore as much as 2,400 feet in vertical dimension are present (Cook, 1957, p. 63-70).
The common ore minerals of the replacement deposits are galena, sphalerite, argentite, enargite, and tetrahedrite. Oxidation of these deposits extends to depths of 2,000 feet and is marked by accumulations of malachite, azurite, chrysocolla, covellite, anglesite, cerussite, smithsonite, calamine, hydrozincite, cerargyrite, native silver, and plumbo-jarosite. Ore minerals of the fissure veins are chiefly enargite, argentite, and galena, and minor amounts of sphalerite, chalcopyrite, arsenopyrite, and tetrahedrite are present. Gangue minerals are pyrite, quartz, calcite, and barite (Cook, 1957, p. 70-71).
Both types of ore deposits are associated with bands of hydrothermal alteration. Near fissure veins, the rocks are impregnated with pyrite, jas-peroid, barite, and sericite; the replacement deposits are surrounded by zones of jasperoid, clay minerals, dolomite, pyrite, and sericite (F. H. Howd, in Cook, 1957, p. 124-134).
Native gold is a rare constituent of the Tintic ores, though some oxidized ore shoots of the Mammoth mine contained flakes of native gold associated with jasperoid and quartz. Most of the gold is recovered from ore containing abundant enargite (Lindgren and Loughlin, 1919, p. 142).
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