Porphyry Mo Mineralization Research Articles

S, C, Sr, and Pb sources in the Pliocene Silver Creek porphyry, Mo system Rio, Colorado

The Pliocene Silver Creek porphyry Mo deposit at Rico, southwest Colorado, is the youngest known porphyry Mo deposit in the Colorado mineral belt. Associated sulfate replacement deposits, epithermal Pb-Zn-Ag vein and replacement deposits, and Recent hot springs also occur. We investigated the S, C, Sr, and Pb sources at the various levels of this well-preserved hydrothermal system by isotopic studies of the mineralization, and of sedimentary and igneous rocks in the area.Hydrothermal sulfide delta 34 S values are tightly grouped at ca. 0 per mil (x = 0.3 + or - 2.0ppm, 1Sigma ; n = 107) and are substantially lower than those of the hydrothermal sulfates (x = 15.2 + or - 1.6ppm, 1Sigma ; n = 14). Pliocene hydrothermal carbonate delta 13 C values (-7.9 to +1.1; x = -4.9 + or - 2.7ppm, 1Sigma ; n = 16) are similar to those for the Pennsylvanian Hermosa Formation carbonate (delta 13 C = -6.7 to +2.6ppm; x = -3.0 + or - 3.2, 1Sigma ; n = 5), which hosts most of the base and precious metal mineralization, whereas Recent hot spring tufas have somewhat higher values (delta 13 C = 1.8-5.5ppm; x = 3.7 + or - 1.3ppm, 1Sigma ; n = 5). Pliocene hydrothermal carbonates have delta 18 O values between -5.1 and 12.3 per mil (x = 5.0 + or - 6.3ppm, 1Sigma ; n = 16). The tufas have higher delta 18 O values (x = 15.4 + or - 2.6ppm, 1Sigma ; n = 5).Hydrothermal carbonates (including tufa) and sulfate have initial 87 Sr/ 86 Sr (sub (i)) values between 0.70700 and 0.71168. Pennsylvanian sedimentary rocks in the Rico district had 87 Sr/ 86 Sr ratios between 0.70877 and 0.71694 at the time of mineralization. Fresh and altered Pliocene monzonite intrusions at Rico have initial 87 Sr/ 86 Sr (sub (4)) values of 0.70581 and 0.70563, respectively, whereas variably altered rholite dikes have initial 87 Sr/ 86 Sr (sub (4)) values of 0.70987, 0.71574, and 0.71716. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 206 Pb/ 204 Pb ratios of molybdenite, pyrite, and galena taken together are 18.27 to 19.65, 15.55 to 15.70, and 37.75 to 38.62. Pliocene lamprophyre and rhyolite dikes at Rico have equivalent Pb isotope ratios of 18.26, 15.48, and 37.81 and 18.79, 15.65, and 38.02, respectively. These Pb isotope data are typical of Tertiary volcanic rocks and associated sulfides in southwest Colorado.Our delta 34 S data indicate a magmatic S source for the porphyry Mo and epithermal base metal sulfide mineralization. Most of the sulfide Pb is also of magmatic origin. In contrast, hydrothermal sulfate replacement deposits peripheral to the porphyry Mo deposit, carbonate gangue from the base metal deposits, and the Recent hot spring tufa derived their respective S, C, and Sr from local sedimentary rocks. Our delta 18 O data indicate that the hydrothermal carbonates were deposited from 18 O-shifted meteoric waters. Our comprehensive isotopic data set presents a similar genetic picture to that of other molybdenite deposits in the mineral belt, in that the porphyry Mo mineralization was dominated by magmatic components, whereas the peripheral base metal mineralization contains both magmatic and upper crustal components. These important genetic similarities are independent of fundamental differences in tectonic setting.

Volatile transport in a convecting magma column: Implications for porphyry Mo mineralization

Research Article| December 01, 1995 Volatile transport in a convecting magma column: Implications for porphyry Mo mineralization Hiroshi Shinohara; Hiroshi Shinohara 1Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, 305, Japan Search for other works by this author on: GSW Google Scholar Kohei Kazahaya; Kohei Kazahaya 1Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, 305, Japan Search for other works by this author on: GSW Google Scholar Jacob B. Lowenstern Jacob B. Lowenstern 2U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Geology (1995) 23 (12): 1091–1094. https://doi.org/10.1130/0091-7613(1995)023<1091:VTIACM>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hiroshi Shinohara, Kohei Kazahaya, Jacob B. Lowenstern; Volatile transport in a convecting magma column: Implications for porphyry Mo mineralization. Geology 1995;; 23 (12): 1091–1094. doi: https://doi.org/10.1130/0091-7613(1995)023<1091:VTIACM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We propose that convection in a column of silicic magma allows transport of volatile components from large (>50 km3) magma chambers to the sites of shallow (≈3 km) porphyry-type Mo deposits. Using constraints from the Henderson and Pine Grove systems, we show that even at temperatures as low as 700 °C, a granitic magma with 30 vol% phenocrysts can flow through a magma column with a 150 m radius at a rate >10 km3/yr—enough magma to contribute the Mo necessary to form an ore deposit in a geologically reasonable time frame. This process requires an efficient mechanism for bubble separation at the top of the magma column to produce degassed magma that can descend down through the column. It also requires slow rates of crystallization in the silicic magma, consistent with experimental studies. Hydrothermal fluids released from the convecting magma column can explain many geologic features of the deposits. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

F51 火道内マグマ対流による脱ガス : 斑岩 Mo 鉱床の生成

F51 火道内マグマ対流による脱ガス : 斑岩 Mo 鉱床の生成

Geological setting and styles of mineralization, north arm of Sulawesi, Indonesia

The north arm of Sulawesi consists of a Neogene island arc (North Sulawesi Arc) built upon Paleogene volcanic-sedimentary basement and underlain by oceanic crust, which is followed to the west by an arcuate, highly deformed terrane (neck of Sulawesi) characterized by metamorphic rocks and felsic granitoids belonging to the Sundaland continental margin. These two terranes have been contiguous during the Tertiary. The evolution of the North Sulawesi Arc is divided into two stages separated by collision of the north arm with the Sula Platform microcontinent in mid-Miocene time. During the Early Miocene a calc-alkaline andesitic arc developed in relation to west-directed subduction. Arc-continent collision resulted in back-arc thrusting, clockwise rotation of the north arm, and inception of subduction along the North Sulawesi Trench. Post-collisional magmatism in the North Sulawesi Arc produced felsic to mafic volcanic suites that are thought to be related primarily to rifting of the former arc rather than directly to subduction. In the neck of Sulawesi,LILE and LREE-element enriched, potassic granites (Dondo suite) of continental affinity (Sr 87/Sr 86 0.71) were generated. The north arm of Sulawesi is comparatively well mineralized. Porphyry CuAu and porphyry Mo mineralization is approximately 2–4 Ma old based on preliminary KAr dating and geological relationships. The former developed in an oceanic terrane following collision-related arc reversal, whereas the latter developed in a continental terrane that underwent lower crustal melting during extension following the same collision. Porphyry CuAu mineralization in the North Sulawesi Arc is associatedwith clusters of small hornblende diorite or quartz diorite stocks, but the specific volcanic environment above these intrusions and their magmatic affinity remain unknown. Mineralization related to porphyry CuAu districts includes CuAu skarn, polymetallic vein and high sulphidation epithermal Au (+enargite). Porphyry Mo mineralization in the neck of Sulawesi is related to small stocks or roof apophyses of the Dondo batholith. Cogenetic granites are exposed over 5000 km 2 and are intruded in an arcuate belt, more than 400 km long, parallel to the Sula Platform collision zone. Unimodal felsic volcanics of Plio-Pleistocene age, which occur locally along the inner side of the north arm and further to the south, are probably the extrusive equivalents of the Dondo granites. Epithermal Au mineralization (typically quartz-calcite veins ± adularia) is associated mainly with the Early Miocene andesitic arc but there are important exceptions, and in general the age of mineralization is poorly known. A district-wide correlation between epithermal Au mineralization and porphyry CuAu mineralization is not apparent. The most important epithermal Au district (Kotamobagu) is inferred to be associated with a long-lived volcanic center represented by the Moat caldera. Epithermal gold systems in the North Sulawesi Arc are generally eroded deeply, typically with chlorite-epidote wallrock alteration, and little is known about their associated volcanic environment. In addition to high sulphidation Au mineralization related to porphyry systems, other styles and settings of Au mineralization in the north arm are exemplified by the Gunung Pani rhyolitic dome, the Patung diatreme breccia, the Mesel jasperiod, hosted partly by carbonate rocks, and sedimentary replacement Au-base metal mineralization at Doup. Diversity of mineralization in the north arm is further illustrated by VMS mineralization in volcanic basement to the Neogene arc, and by metamorphogenic quartz vein Au mineralization in the neck of Sulawesi.

Volcanic and intrusive history of the Pine Grove porphyry molybdenum system, southwestern Utah

The Pine Grove porphyry molybdenum deposit in the Wah Wah Mountains, southwestern Utah, occurs in the eroded vent of a lower Miocene ash flow (23-22 m.y. old). The vent, located in a tilted basin-and-range fault block, has been eroded about 1.7 km below the pre-eruption surface; consequently, the closest outcrops of related ash-flow tuff are 10 km away from the vent. Correlation of comagmatic ash-flow tuff and intrusive porphyry is made possible by the presence of accessory almandine-spessartine garnet of unique composition in both extrusive and intrusive units.Several lines of evidence suggest the presence of a parental magma chamber roughly 100 km 3 in size and compositionally zoned from rhyolite to dacite. Each eruptive episode began with a high silica content, rhyolitic magma containing quartz, sanidine, plagioclase, biotite, garnet, titanomagnetite, monazite, xenotime, ilmenorutile (?), and zircon. Presumably in response to continued rapid eruption and deeper drawdown in the parent chamber, some ash-flow eruptions also vented dacitic magma containing quartz, plagioclase, sanidine, biotite, hornblende, augite, titanomagnetite, ilmenite, sphene, apatite, and zircon.The dominant ore-related intrusion was emplaced immediately following concurrent intrusion of rhyolitic and dacitic magma into the vent. Multiple injections of trachyandesitic magma into the base of the chamber may have initiated convection or magma fracturing, surging of dacitic magma, and exsolution of volatiles that resulted, first, in ash-flow eruptions and, later, in episodes of mineralization. Therefore, an unusual combination of eruption mechanics and chamber volume and geometry allowed sampling of possibly the entire compositional range of the chamber during eruption but prohibited the complete loss of rhyolitic magma. Magmatic processes, such as late-stage convection, magma fracturing, and volatile fluxing may have been critical in the development of porphyry Mo mineralization.