COMPLEX RESISTIVITY SPECTRA OF PORPHYRY COPPER MINERALIZATION

Geophysics ◽  
1973 ◽  
Vol 38 (1) ◽  
pp. 49-60 ◽  
Author(s):  
G. D. Van Voorhis ◽  
P. H. Nelson ◽  
T. L. Drake
Keyword(s):  
Porphyry Copper ◽  
Step Response ◽  
Frequency Effect ◽  
Volume Distribution ◽  
Porphyry Copper Deposits ◽  
Frequency Range ◽  
Complex Resistivity ◽  
Copper Mineralization ◽  
Porphyry Copper Mineralization ◽  
Geometric Effects

Complex resistivity spectra, in the frequency range 0.001 to 10 hz, have been obtained through computer analysis of waveforms tape recorded at porphyry copper deposits. When care is taken to avoid distortions caused by the geometric effects of electrical inhomogeneities, the spectra of typical porphyry copper mineralization are remarkably uniform in character. The geometric effects of veins, which generally complicate the response of hand samples, can be reduced through in‐situ measurements using electrode separations of a few meters. In the frequency range of interest for inducedpolarization (IP) exploration, the observed spectra are accurately described by [Formula: see text] where K is a constant and b is a positive fraction. The fraction b has a value less than 0.1 and is a complete measure of IP. In the frequency range of interest, Laplace transformation gives the step response to be approximated by [Formula: see text] Typical current waveforms used in IP prospecting can be synthesized by superposition of steps. Using these frequency and time response functions, percent frequency effect, phase, and pulse‐transient parameters are compared as measures of IP. By using a volume distribution function, it is shown that a distribution of lossy capacitors will explain the observed response. Physically, this might correspond to the double‐layer capacitance of metallic particles in mineralized rock.

HYPOGENE ALUNITE FROM THE EL SALVADOR DISTRICT, CHILE, INDICATES POTENTIAL FOR A BLIND PORPHYRY COPPER CENTER

2020 ◽  
Vol 115 (2) ◽  
pp. 231-239 ◽  
Author(s):  
Jeffrey W. Hedenquist ◽  
Yasushi Watanabe ◽  
Antonio Arribas
Keyword(s):  
El Salvador ◽  
Porphyry Copper ◽  
Copper Deposit ◽  
Hydrothermal Activity ◽  
Porphyry Copper Deposits ◽  
Copper Ore ◽  
Copper Mineralization ◽  
Alteration Minerals ◽  
Porphyry Copper Mineralization ◽  
Granodiorite Porphyry

Abstract Surface samples of hypogene alunite that cement late breccia bodies from the El Salvador porphyry copper district of Chile were recently dated. One alunite sample over the principal Turquoise Gulch porphyry deposit has a 40Ar/39Ar total gas age of 40.64 ± 1.04 Ma, overlapping the age of a late latite intrusion. Two other samples associated with quartz-alunite replacement of rhyolite, ~750 m southwest of the collapse zone over the block cave of the porphyry copper deposit, are distinctly younger, at 38.12 ± 0.66 and 38.04 ± 0.22 Ma (averages of duplicate analyses, with ±2σ errors). Previously reported U/Pb ages of zircons from 15 Eocene-age diorite, granodiorite, and granite porphyry intrusions have weighted mean ages that range from about 44 to 41 Ma, with peak magmatic flux interpreted at 44 to 43 Ma. Porphyry copper ores in the El Salvador district formed at about the same time as porphyry intrusions, with intrusive centers that migrated in a south-southwest direction, from the small deposits at Cerro Pelado (~44.2 Ma), to Old Camp (~43.6 Ma) and M Gulch-Copper Hill (~43.5–43.1 Ma), to the main ore deposit at Turquoise Gulch (~42 Ma). The granodiorite porphyry intrusions at Turquoise Gulch are associated with ~80% of the known copper ore of the district; they record waning stages of magmatism at 42.5 to 42.0 Ma, followed by weakly altered latite dikes at 41.6 Ma. Molybdenite in quartz veins returned Re-Os ages of 41.8 to 41.2 Ma. The two alunite samples from our study with coincident dates of ~38 Ma provide evidence for magmatic-hydrothermal activity younger than any recognized to date, consistent with the alteration overprint of quartz-alunite on older muscovite after erosion. This younger activity must have been associated with a blind intrusion, likely located south of the Turquoise Gulch deposit, based on the distribution of alteration minerals, and offset from the zoning associated with the Turquoise Gulch center. Stable isotope values (δ34S, δ18O, δD) of the ~38 Ma alunite indicate a high-temperature hypogene origin, consistent with formation in a lithocap environment that typically is located at shallow levels over and on the shoulders of porphyry copper deposits. Both observations—alteration overprint and markedly younger age of alunite—indicate the potential for porphyry copper mineralization south of Granite Gulch, as much as 1,000 m below the level of the coeval outcropping quartz-alunite replacement, perhaps near ~2,000-m elevation; this is hundreds of meters deeper than the known copper ore of Turquoise Gulch.

Geochronology of mid-Cretaceous to Eocene magmatism, Babine porphyry copper district, central British Columbia

2001 ◽  
Vol 38 (4) ◽  
pp. 639-655 ◽  
Author(s):  
D G MacIntyre ◽  
M E Villeneuve
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Porphyry Copper ◽  
Volcanic Rocks ◽  
Porphyry Copper Deposits ◽  
Isotopic Dating ◽  
Plate Convergence ◽  
Copper Mineralization ◽  
Porphyry Copper Mineralization ◽  
Magmatic Event

New U/Pb and 40Ar/39Ar isotopic dating in the Babine porphyry copper district of central British Columbia documents three distinct magmatic events at 107–104, 85–78, and 54–50 Ma. The earliest event involved emplacement of rhyolite domes into submarine volcanic rocks of the Rocky Ridge Formation. The rhyolite domes and related dacitic to basaltic volcanic rocks gave a U–Pb age of 107.9 ± 0.2 Ma and an 40Ar/39Ar age of 104.8 ± 1.2 Ma. The rhyolites, which were previously mapped as Eocene, are reinterpreted to be part of a previously unrecognized mid-Cretaceous cauldron subsidence complex. The regionally extensive Late Cretaceous magmatic event is also recognized in the Babine district and is represented by 40Ar/39Ar ages of 85.2 ± 2.8 and 78.3 ± 0.8 Ma on two Bulkley intrusions, one of which has associated porphyry copper mineralization. The final magmatic event is the most widespread and involved emplacement of the Babine intrusions and formation of numerous porphyry copper deposits including the Bell and Granisle past producers. Twenty-one new 40Ar/39Ar isotopic ages for these intrusions and coeval andesites of the Newman Formation have a narrow range from 53.6 ± 0.9 to 49.9 ± 0.6 Ma, whereas previous K–Ar isotopic dating had a possible range of 15 Ma. The mid-Cretaceous, Late Cretaceous, and Eocene magmatic suites in the Babine district are interpreted to be part of a long-lived volcano-plutonic complex that was the site of periodic magmatism and porphyry copper mineralization over a 60 Ma time period. This complex may have evolved within a zone of extension (pull-apart basins) situated between dextral strike-slip faults that were active during periods of rapid oblique plate convergence.

Complex resistivity spectra of porphyry copper mineralization [letter]

Geophysics ◽  
1973 ◽  
Vol 38 (5) ◽  
pp. 984-984 ◽  
Author(s):  
P. H. Nelson ◽  
G. D. Van Voorhis
Keyword(s):  
Time Domain ◽  
Porphyry Copper ◽  
Voltage Response ◽  
Complex Resistivity ◽  
Copper Mineralization ◽  
Porphyry Copper Mineralization ◽  
The Time Domain

Our equations (14), (15), and (16), for the time-domain voltage response of IP, have recently been found to be in error. Rather than giving corrections to the original equations, we offer the more compact versions

New U–Pb and Re–Os geochronology of Laramide porphyry copper mineralization along the Cananea lineament, northeastern Sonora, Mexico: Contribution to the understanding of the Cananea copper district

2017 ◽  
Vol 81 ◽  
pp. 1125-1136 ◽  
Author(s):  
Rafael Del Rio-Salas ◽  
Lucas Ochoa-Landín ◽  
Martín Valencia-Moreno ◽  
Thierry Calmus ◽  
Diana Meza-Figueroa ◽  
...  
Keyword(s):  
Porphyry Copper ◽  
Copper Mineralization ◽  
Porphyry Copper Mineralization

scholarly journals Mineral markers of porphyry copper mineralization: progress report on the evaluation of tourmaline as an indicator mineral

2018 ◽  
Author(s):  
M B McClenaghan ◽  
C E Beckett-Brown ◽  
M W McCurdy ◽  
A M McDonald ◽  
M I Leybourne ◽  
...  
Keyword(s):  
Porphyry Copper ◽  
Progress Report ◽  
Copper Mineralization ◽  
Indicator Mineral ◽  
Porphyry Copper Mineralization

Geochemical evidence for magmatic fluids in porphyry copper mineralization

1982 ◽  
Vol 78 (4) ◽  
pp. 404-412 ◽  
Author(s):  
D. A. F. Hendry ◽  
A. R. Chivas ◽  
S. J. B. Reed ◽  
J. V. P. Long
Keyword(s):  
Porphyry Copper ◽  
Geochemical Evidence ◽  
Copper Mineralization ◽  
Magmatic Fluids ◽  
Porphyry Copper Mineralization
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