Torshab Mine Stone

By Dennis P. Cox
DESCRIPTION This generalized model includes various subtypes all of which contain chalcopyrite in
stockwork veinlets in hydrothermally altered porphry and adjacent country rock (see fig. 50).
GENERAL REFERENCE Titley (1982).
GEOLOGICAL ENVIRONMENT
Rock Types Tonalite to monzogranite or syenitic porphyry intruding granitic, volcanic, calcareous
sedimentary, and other rocks.
Textures Porphyry has closely spaced phenocrysts and microaplitic quartz-feldspar groundmass.
Age Range Mainly Mesozoic and Cenozoic, but may be any age.
Depositional Environment High-level intrusive rocks contemporaneous with abundant dikes, breccia
fipes, faults. Also cupolas of batholiths.
Tectonic Setting(s) Rift zones contemporaneous with Andean or island-arc volcanism along
convergent plate boundaries. Uplift and erosion to expose subvolcanic rocks.
Associated Deposit Types Base-metal skarn, epithermal veins, polymetallic replacement, volcanic
hosted massive replacement. See also: Porphyry Cu-skarn related, porphyry Cu-Mo, and porphyry Cu-
Au.

DEPOSIT DESCRIPTION
Mineralogy: Chalcopyrite + pyrite ± molybdenite; chalcopyrite + magnetite ± bornite ± Au;
assemblages may be superposed. Quartz + K-feldspar + biotite ± anhydrite; quartz + sericite + clay
minerals. Late veins of enargite, tetrahedrite, galena, sphalerite, and barite in some deposits.
Texture/Structure Stockwork veinlets and disseminated sulfide grains.
Alteration From bottom, innermost zones outward: sodic-calcic, potassic, phyllic, and argillic to
propylitic. High-alumina alteration in upper part of some deposits. See table 3. Propylitic or
phyllic alteration may overprint early potassic assemblage.
Ore Controls Stockwork veins in porphyry, along porphyry contact, and in favorable country rocks
such as carbonate rocks, mafic igneous rocks, and older granitic plutons.
Weathering Green and blue Cu carbonates and silicates in weathered outcrops, or where leaching is
intense, barren outcrops remain after Cu is leached, transported downward, and deposited as
secondary sulfides at water table or paleowater table. Fractures in leached outcrops are coated
with hematitic limonite having bright red streak. Deposits of secondary sulfides contain
chalcocite and other CU2S minerals replacing pyrite and chalcopyrite.
Residual soils overlying
deposits may contain anomalous amounts of rutile.
Geochemical Signature: Cu + Mo ± Au + Ag + W + B + Sr center, Pb, Zn, Au, As, Sb, Se, Te, Mn, CO,
Ba, and Rb outer. Locally Hi and Sn form most distal anomalies. High S in all zones. Some
deposits have weak U anomalies.
EXAMPLES
Bingham, USUT
(Lanier and others, 1978)
San Manuel, USAZ
(Lowell and Guilbert, 1970)
El Salvador, CILE
(Gustafson and Hunt, 1975)

GRADE AND TONNAGE MODEL OF PORPHYRY CU
By Donald A. Singer, Dan L. Mosier, and Dennis P. Cox
COMMENTS All porphyry copper depositswith available grades and tonnages were included in these
- order to provide a model for cases where it is not possible to use the gold-rich or
molybdenum-rich models. Parts of the porphyry copper deposits which could be considered skarn
were included in these data. Gold grade is correlated with tonnage (r = -0.49, n = 81) and with
molybdenum grade (r = -0.45, n = 55).See figs. 51-530





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