New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/13 Geological Notes on the Miami-Inspiration Mine E. F. Reed and W. W. Simmons, 1962, pp. 153-157 in: Mogollon Rim Region (East-Central Arizona), Weber, R. H.; Peirce, H. W.; [eds.], New Mexico Geological Society 13th Annual Fall Field Conference Guidebook, 175 p. This is one of many related papers that were included in the 1962 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. 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The story of the Miami-Inspiration ore body has many There is no constant system of orientation of veinlets in the chapters. It has been the scene of many innovations in intrusives. mining and metallurgy and its stories are well covered in In common with most of the other porphyry copper Parsons The Porphyry Coppers. deposits, there is a three-fold vertical division in the ore- Miami Copper Company was incorporated in 1908, body. A leached zone overlies a zone of supergene en- and made its first production in 1911. Inspiration Consoli- richment. The latter zone averages about 300 feet in dated Copper Company was incorporated in 1911 to con- thickness. Below it is the protore, which in general is too solidate the properties of the Inspiration Copper Company low in grade to be mineable. and the Live Oak Development Company. Production be- ROCK DESCRIPTIONS gan in 1915. Precambrian Rocks Production at Miami has been entirely from under- Pinal Schist. This unit consists of a series of meta- ground mining and in-place leaching. During the period morphosed sedimentary and volcanic rocks of early Pre- 1911-1925, production amounted to 24,400,000 tons aver- cambrian age. aging about 2% copper. From 1925 to 1959, production The general strike of the schistosity is about N50°E, was from the low-grade ore bodies. Total production was and the dip is usually steeply southeast. There are many 159,000,000 tons, which yielded in excess of 2,300,000,- variations, however. The series is composed of a coarse- 000 pounds of copper. Production since 1959 has been grained quartz-muscovite schist, and a fine-grained quartz- from in-place leaching at the rate of about 1,500,000 sericite-chlorite variety with some fine-grained amphibole pounds of copper per month. In June, 1960, Miami Cop- schist. The units are not usually mapped separately. per Company was liquidated. Since that date, the prop- Pioneer Formation. The Pioneer formation was origi- erty has been operated as the Miami Copper Company, nally called the Pioneer shale by Ransome (1919). It is Division Tennessee Corporation. part of the Apache group of Precambrian age, but is young- As stated, Inspiration began production in 1915. er than the Pinal schist. The basal part is a pebbly arkose Until 1948, all production was from underground mining. 15-20 feet thick. This grades into hard, fine-grained red- From 1948 to 1954, production was from both underground dish-brown arkosic sandstone which, in some localities, and open-pit operations. Since 1954, all production has grades into fine-grained sandstone and arenaceous shale. been from open-pit operations: Inspiration was the first Tertiary Rocks of the porphyry coppers to use only a flotation mill for Diabase. The age of the diabase shown on the map recovery. This mill continued in operation until 1932. In (Fig. 1) is not definitely established; however, some is be- 1926 an acid ferric-sulphate plant, unique in the industry, lieved to be of Tertiary age. It is dark gray or dark was put into operation for the recovery of copper from greenish gray, and ranges in texture from aphanitic to mixed oxide and sulphide ore. In 1956, the re-equipped coarse grained. The composition ranges from augite dia- concentrator was placed in operation, and copper is now base to hornblende diabase. recovered by a dual process of leaching followed by flota- Willow Springs Granite. This granite is gray and tion. Production up to January 1, 1962, totaled 175,- finer grained than the usual granite. It consists of abun- 374,531 tons which yielded 3,322,124,665 pounds of dant quartz and microcline, with oligoclase, muscovite and copper. biotite. Accessory minerals are apatite and tourmaline, GENERAL GEOLOGY but they are not abundant. As shown on the accompanying map and section Schultze Granite. This granite is more correctly des- (Fig. 1), the Miami-Inspiration ore body has a strike ignated as a porphyritic quartz monzonite. Large ortho- length of slightly over 12,000 feet. Its width ranges clase phenocrysts 1 to 4 inches long are set in a coarse from 1000 to 2500 feet and averages nearly 2000 feet. matrix composed of quartz, oligoclase, orthoclase and bio- The thickness or height ranges from 40 to 700 feet. Al- tite. Accessory minerals, magnetite, apatite and sphene, though mined as separate entities and severed by faults, are sparse. It weathers to a pale yellow. it is essentially one zone of mineralization, and thus is one Granite Porphyry. This is considered to be a phase of the great ore bodies of the world. of the Schultze granite, but it is distinctly later intrusion. The general trend of its strike is east-northeast. It It is porphyritic with a nearly aphanitic groundmass, con- lies along the northern contact of a prominent bulge of spicuous quartz phenocrysts, and biotite, oligoclase, and intrusive igneous rock. Ore-grade mineralization is in orthoclase constituting the remainder of the phenocryst schist, granite, and granite porphyry. In general, the fraction. It generally weathers light gray. schist-intrusive contact dips steeply to the south. Whitetail Conglomerate. The Whitetail conglomer- In the east end of the orebody, mineralization tends ate consists of detrital components of considerable variety. to follow the northeast trend of the schistosity. Farther In general, it does not occupy large areas of outcrop. west, the sulphide veinlets tend to cut across the schist- Dacite. The dacite has an aphanitic or glassy • Z 1: //‘ • --. 4,i - , • i " " • • , ., 0T9 _ . i\. ;/ / T6 9 s ' S ‘ • r; ft v " ' ' „s Tsti 1\9Fv ( s „ , . v-•:---48 ....,, , ' , N N so. v v v ( ' v v .,, , S • n ° 10+9 . 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