ACID ROCK DRAINAGE PREDICTION FOR HOST ROCKS OF PORPHYRY COPPER DEPOSITS IN THE BAIMKA ORE TREND (STATIC AND KINETIC TESTS)

SummaryThe accessory minerals rutile and apatite have been studied in 77 known porphyry copper deposits. Their value as indicators has been well established on the basis of specific chemical and paragenetic variations which they show.Rutile occurs as the only Ti-mineral in the quartz-sericite zone, is dominant in the biotite-orthoclase zone, and is generally found in the inner fringes of the chlorite-epidote zone. It forms in these zones mainly as a result of the destruction of sphene, but also from biotite and hornblende.The length: width ratio of rutile crystals is 1·5:1 in the centre of a porphyry system, increasing gradually outward to 2:1. A characteristic red colour displayed in thin section is attributed to a high copper content ranging from 100 to 500 ppm. The ratio of Cr+V:Nb+Ta is also unusually high.Apatite shows evidence of a complicated history of corrosion and redeposition accompanied by outward migration during the life of the porphyry system. The migration parallels that of copper and typically extends far into the host rocks. The apatite is enriched in chlorine. A plot of a versus c shows a clear separation of apatites of various genetic types, including tin and molybdenum porphyries.

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EXPERIMENTAL MODELING OF THE «WATER-SOLID PHASE» INTERACTION DURING THE WEATHERING OF THE HOST ROCKS OF PORPHYRY COPPER DEPOSITS

The Geological Evolution of the Water-Rock Interaction ◽

10.31554/978-5-7925-0536-0-2018-280-283 ◽

2018 ◽

Author(s):

D. A. Yablonskaya ◽

T. N. Lubkova ◽

T. V. Shestakova ◽

I. Yu. Nikolaeva

Keyword(s):

Solid Phase ◽

Porphyry Copper ◽

Experimental Modeling ◽

Phase Interaction ◽

Porphyry Copper Deposits ◽

Copper Deposits ◽

Host Rocks

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The Origins of Sulfate in Cenozoic Non-Marine Evaporites in the Basin and-Range Province, Southwestern North America

Geosciences ◽

10.3390/geosciences11110455 ◽

2021 ◽

Vol 11 (11) ◽

pp. 455

Author(s):

Ailiang Gu ◽

Christopher John Eastoe

Keyword(s):

North America ◽

Acid Rock Drainage ◽

Porphyry Copper ◽

Copper Deposit ◽

Porphyry Copper Deposits ◽

Basin And Range Province ◽

Acid Rock ◽

Supergene Enrichment ◽

Younger Age ◽

Source Materials

Cenozoic evaporites (gypsum and anhydrite) in southwestern North America have wide ranges of δ34S (−30 to +22‰; most +4 to +10‰) and δ18OSO4 (+3 to +19‰). New data are presented for five basins in southern Arizona. The evaporites were deposited in playas or perennial saline lakes in closed basins of Oligocene or younger age. Very large accumulations in Picacho, Safford and Tucson Basins have isotope compositions plotting close to a linear δ34S-δ18OSO4 relationship corresponding to mixing of two sources of sulfur: (1) sulfate recycled from Permian marine gypsum and (2) sulfate from weathering of Laramide-age igneous rocks that include porphyry copper deposits. In the large evaporites, sulfate with δ34S > +10‰ is dominantly of Permian or Early Cretaceous marine origin, but has locally evolved to higher values as a result of bacterial sulfate reduction (BSR). Sulfate with δ34S < −10‰ formed following exposure of sulfides, possibly formed during supergene enrichment of a porphyry copper deposit by BSR, and have values of δ18OSO4 higher than those of local acid rock drainage because of participation of evaporated water in BSR. Accumulations of 30 to 100 km3 of gypsum in Picacho and Safford Basins are too large to explain as products of contemporaneous erosion of Permian and Laramide source materials, but may represent recycling of Late Cretaceous to Miocene lacustrine sulfate.

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