On the relationship between whole rock chemistry and porphyry copper mineralization

Mason, D. R.; Feiss, P. Geoffrey

doi:10.2113/gsecongeo.74.6.1506

Cited by 12 publications

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“…Using the normative corundum content of intrusions as a measure of the alumina/alkali ratio, Feiss (1978) showed that mineralized Laramide-age intrusions of the southwestern United States contain on the average 2.5 wt% more corundum compared to non-mineralized intrusions. Mason and Feiss (1979) showed that the same relationship holds for intrusions in the southwest Pacific porphyry copper belt. These workers also noted that within an intrusive center, the alumina/ alkali ratio varies significantly, with the rocks having the highest ratio being most closely associated with the mineralization event.…”

Section: K Yang and R J Bodnarmentioning

confidence: 75%

Magmatic-Hydrothermal Evolution in the “Bottoms” of Porphyry Copper Systems: Evidence from Silicate Melt and Aqueous Fluid Inclusions in Granitoid Intrusions in the Gyeongsang Basin, South Korea

Yang

Bodnar

1994

International Geology Review

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The Gyeongsang Basin of southeastern Korea contains numerous Cretaceous-early Tertiary (120-40 Ma) granitoid intrusions formed at a convergent plate boundary. The geotectonic setting is similar to that associated with porphyry-type mineralization elsewhere in the Circumpacific region. However, erosion has removed higher-level economic mineralization and exposed deeper levels of the granitoids, representing the poorly mineralized "bottoms" of porphyry copper systems. The intrusions of the Gyeongsang Basin thus provide a unique opportunity to advance our understanding of magmatic-hydrothermal evolution in the roots of porphyry-type systems, below the level of economic mineralization.The physical and chemical environment during crystallization of the magmas has been characterized through studies of silicate melt and aqueous fluid inclusions in the granitoids. Two different types of silicate melt inclusions were recognized based on occurrence and roomtemperature appearance. Type-I inclusions contain one or more crystalline phases and vapor; type-II inclusions consist of a cluster of small crystals, partially devitrified glass, and vapor. Petrographic and Raman analyses indicate that most silicate melt inclusions contain muscovite daughter crystals. Some also contain feldspar. Solidus temperatures of type-I inclusions in quartz phenocrysts range from '^SO to 650 ° C, whereas solidus temperatures of type-I and type-II inclusions in vug quartz are slightly higher (640-670° C). Liquidus temperatures span a much wider range compared to solidus temperatures, with maximum liquidus temperatures of melts in phenocrysts being slightly higher (<930° C) than those in vug quartz (<910° C).Three types of aqueous inclusions were observed based on occurrence and room temperature phase proportions. Type-A inclusions are liquid rich and low to moderate in salinity; type-B inclusions are vapor rich and low in salinity; type-C inclusions are liquid rich and contain a halite daughter mineral. Some type-A inclusions with a salinity of approximately 25 wt% NaCl equivalent are spatially associated with silicate melt inclusions in phenocrysts, where they occur as three-dimensional clusters of tiny inclusions surrounding the silicate melt inclusion. Type-A inclusions also occur along fractures in quartz phenocrysts. Non-fracture-controlled type-C inclusions are rare in phenocryst quartz, but are common in vug quartz, where they are associated with silicate melt inclusions. Type-C inclusions that coexist with silicate melt inclusions generally homogenize by halite dissolution after the vapor bubble and show a wide range in salinity, from about 30 to >60 wt% NaCl equivalent. Coexisting halite-bearing (Type-C) and vapor-rich (Type-B) inclusions in phenocryst quartz suggest local immiscibility in the lateor post-magmatic fluid.Pressure-temperature conditions during the final stages of magmatic-hydrothermal activity associated with the granitoid intrusions of the Gyeongsang Basin were approximately 630 ° to 670° C and 1.9 to 2.5 kbars. These resul...

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Section: K Yang and R J Bodnarmentioning

confidence: 75%

Magmatic-Hydrothermal Evolution in the “Bottoms” of Porphyry Copper Systems: Evidence from Silicate Melt and Aqueous Fluid Inclusions in Granitoid Intrusions in the Gyeongsang Basin, South Korea

Yang

Bodnar

1994

International Geology Review

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“…They found no single element capable of discriminating the two groups but noted that, when different rock types are present in a district, the porphyry copper deposits are associated with late, low potassium intrusions. An interesting extension of this work was the suggestion by Mason and Feiss (1979) that productive intrusions were characterized by low ratios of A1203/(K20 q-Na20 q-CaO). There is, nonetheless, a significant overlap in this ratio between known productive and nonproductive intrusions.…”

Section: Introduction the Andes Of Central And Northern Chile Containmentioning

confidence: 81%

“…Using data from Mason and McDonald (1978) and Mason and Feiss (1979) (Zentilli, 1974). In this case however, the effect on the discrimination was relatively small.…”

Section: Comparisons With Porphyry Copper Deposits In the Pacific Areamentioning

confidence: 99%

Discrimination of productive and nonproductive porphyritic intrusions in the Chilean Andes

Baldwin¹,

Pearce²

1982

Economic Geology

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A geochemical comparison between productive intrusions (those associated with mineralization) and nonproductive intrusions (those unrelated to mineralization) has been made on the basis of over 100 fresh granitoid rocks from the Chilean porphyry copper belt. The study was carried out on the scale of a mining district (El Salvador-Potrerillos), then on the scale of a single traverse (El Salvador-Chilean coast), and finally on the scale of the Andes itself. The productive intrusions are best characterized by large negative anomalies in Y, Mn, Th, and the heavy rare earth elements. A discriminant diagram of Y against MnO is recommended for predicting whether an apparently fresh intrusion has associated peripheral mineralization.The low values of Y and Mn in productive intrusions can be partly explained by the early crystallization of Y-and Mn-rich hydrous phases such as hornblende and by the loss of Mnrich fluids from the magma. The same elements make useful discriminants in other porphyry copper provinces, although the exact position of the discriminant boundary varies from island arcs through continental margin to continental settings.

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“…Various authors have sought methods to distinguish potentially barren and potentially mineralised intrusions on the basis of factors such as tectono-structural setting, intrusive geometry, petrography, mafic mineral geochemistry, alteration, intrusive structure, and intrusion geochemistry (for example: Chappell and White, 1974;Kestler eta/., 1975;Feiss, 1978;Mason, 1978;Mason and Feiss, 1979;Titley and Beane, 1981;Sillitoe and Gappe, 1984). Methods based on geochemistry of relatively unaltered plutons thought to be prospective for porphyry Cu-Au mineralisation were outlined by Kestler eta/., (1975Kestler eta/., ( ), feiss (1978, Mason (1978) and Mason and Feiss (1979) on the assumption that econom,i'c elements (generally Cu} were originally present in the melt. However, oxygen and hydrogen isotope data on alteration minerals from porphyry copper deposits (forexample:Sheppardeta/., 1969and 1971Sheppard and Taylor, 1974) suggested that the water responsible for porphyry alteration had mixed magmatic/meteoric origins.…”

Section: Discussionmentioning

confidence: 99%

Age, petrology and mineralisation associated with two Neogene intrusive types in the Eastern Highlands of Papua New Guinea

Rogerson¹,

Williamson²

1986

BGSM

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Numerous Neogene porphyritic basic to intermediate intrusive rocks crop out as batholiths, stocks and dyke swarms in the eastern highlands of Papua New Guinea between 144 °E and 146°E. Their radiometric ages range from 18 Ma to 7 Ma, and are consistent with known more definitive stratigraphic relationships. Our work has shown that within this time range, two distinct phases of plutonism occurred and that the second phase from 9 Ma to 7 Ma was often associated with magmatichydrothermal Cu-Au-Ag mineralisation. We have named the earlier phase Akuna-type, and the later phase Elandora-type. Akuna-type intrusives tend to form large complexes (eg. Akuna Intrusive Complex, Bismarck Intrusive Complex) up to 800 km 2 in outcrop area, displaying a wide variety of fractionated compositions from pyroxenite, gabbro, diorite to granodiorite. Other smaller intrusions (Oipo and Kimil Diorites) are more homogeneous. In contrast to Akuna-type, Elandora-type intrusives (Elandora Porphyry, Yandera porphyries) generally form microdioritic, often tabular stocks less than 10 km 2 in area, dykes and dyke swarms, some of which intrude Akuna-type masses. Many bodies and parts of individual bodies display propylitic alteration assemblages, with argillic, phyllic and silicic alteration being locally dominant. Elandora-type intrusives are apparently associated with either areas of outcropping basement or areas underlain at shallow depth by basement. Exposure of many Elandora-type intrusions at the present erosion surface is commonly a function of two fault sets trending 120° and 040°, which intersect to form elevated fault-bound basement blocks and areas of cover underlain at shallow depth by basement. Some Elandora-type intrusions occur in erosional basement highs. The two intrusive types have calc-alkaline affinities. Analysed Elandora-type intrusives have a narrow compositional range between 60 and 70% Si0 2 compared with the wide range of Si0 2 values shown by analysed Akuna-type intrusives. Elandora-type analyses plot on or adjacent to Akuna-type major element variation diagram trend lines at 60% Si0 2 • However, at 60% Si0 2 , Elandora-type intrusives have higher Sr (700 ppm) and lower K,O (< 2%) than Akuna-type intrusives. These empirical geochemical features, coupled with field criteria, serve to distinguish the two intrusive types.

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On the relationship between whole rock chemistry and porphyry copper mineralization

Cited by 12 publications

References 0 publications

Magmatic-Hydrothermal Evolution in the “Bottoms” of Porphyry Copper Systems: Evidence from Silicate Melt and Aqueous Fluid Inclusions in Granitoid Intrusions in the Gyeongsang Basin, South Korea

Magmatic-Hydrothermal Evolution in the “Bottoms” of Porphyry Copper Systems: Evidence from Silicate Melt and Aqueous Fluid Inclusions in Granitoid Intrusions in the Gyeongsang Basin, South Korea

Discrimination of productive and nonproductive porphyritic intrusions in the Chilean Andes

Age, petrology and mineralisation associated with two Neogene intrusive types in the Eastern Highlands of Papua New Guinea

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