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Field, petrochemical, and stable isotope data from peraluminous microgranite dikes and their molybdenite-bearing vugs in the Archean Preissac-Lacorne batholith, Québec, provide evidence for the transport and deposition of molybdenum by an aqueous fluid that exsolved from a felsic magma. A model is proposed in which the microgranite-forming liquid fractionated from a magma that was parental to and intruded less-evolved muscovite monzogranite. Fluid saturation is interpreted to have occurred immediately prior to emplacement, allowing sufficient time for small spherical pockets of fluid to form and rise through the liquid but insufficient time for them to leave the system. These fluid pockets scavenged molybdenum and other components during their migration but were frozen in situ to form molybdenite-bearing vugs as a result of the quenching of the magma. We therefore conclude that the vugs are relicts of the exsolved fluid pockets and that the molybdenite in them reflects the concentration of molybdenum in the fluid, estimated from volumetric relationships to have reached ~7800 ppm. [ABSTRACT FROM AUTHOR]

Numerous skarn-type Sn deposits have been identified in the Nanling Range (South China), of which the Shizhuyuan W-Sn-Bi-Mo, Xianghualing Sn, Jinchuantang Sn-Bi, and Hehuaping Sn deposits are the largest. The Xianghualing deposit, which is the focus of this study, hosts a resource of 0.17 Mt Sn grading 0.93–1.39 wt% SnO2. Whether the distal skarn-type mineralization and the cassiteritesulfide vein-type orebody in the Xianghualing district are genetically related to the Laiziling granitic pluton, which produced the proximal skarn-type Sn mineralization, however, is still unknown. The Xianghualing Sn mineralization occurs exclusively as cassiterite and has been subdivided into four ore-types: (1) lenticular proximal skarn ore (Cst I) containing the mineral assemblage cassiteritepyrrhotite-chalcopyrite-actinolite-wollastonite; (2) layered distal skarn ore (Cst II) containing the mineral assemblage cassiterite-pyrrhotite-chalcopyrite-actinolite; (3) vein cassiterite-sulfide ore (Cst III) distal from the skarn and associated granite containing the mineral assemblage cassiterite-arsenopyrite-pyrrhotite-muscovite-fluorite; and (4) veinlet Sn-Pb-Zn ore (Cst IV) distal from the skarn and associated granite containing the mineral assemblage cassiterite-galena-sphalerite-topaz-quartz. Here, we report the results of in situ laser ablation inductively coupled plasma mass spectrometric (LA-ICP-MS) U-Pb age determinations for garnet from the Xianghualing skarn and the above four types of cassiterite. Our age determinations indicate that there were two independent magmatic-hydrothermal events at ~160 and 156~150 Ma, both of which led to Sn mineralization. The first Sn mineralization event at ~160 Ma (Cst IV U-Pb ages of 159.6 ± 1.4 to 158.5 ± 0.8 Ma) is interpreted to have been associated with a speculative unexposed granitic pluton, which is coeval with the nearby Jianfengling granite intrusion. The second Sn mineralization event at 156~150 Ma (Cst I to Cst III U-Pb ages of 155.9 ± 0.7 to 152.3 ± 1.1 Ma and garnet U-Pb ages of 153.6 ± 7.6 to 151.5 ± 3.5 Ma) is genetically related to the adjacent Laiziling granitic intrusion (152.8 ± 1.2 Ma, zircon U-Pb age). This event was responsible for the bulk of the Sn resource (>95%). Our age determinations provide convincing evidence for superimposed Jurassic Sn mineralizing systems at Xianghualing. They also show the value of combining garnet and cassiterite U-Pb age determinations to constrain the timing of skarn and Sn mineralization and distinguish discrete Sn mineralizing events in a protracted metallogenic history. [ABSTRACT FROM AUTHOR]

Porphyry-type Mo deposits have supplied most of the Mo to the world. However, the source of the Mo and the controls on its enrichment in such deposits is still a matter of great debate. In this study, we present in situ trace element and isotopic data for a giant porphyry Mo deposit (the Chalukou Mo deposit in NE China) and use these data to address these issues. Three primary paragenetic stages of mineralization were recognized at Chalukou: (Stage I) K-feldspar+quartz + minor pyrite (Py-I) + minor molybdenite (Mol-I); (Stage II) quartz + sericite + molybdenite (Mol-II) + pyrite (Py-II); (Stage III) quartz + chlorite + epidote + fluorite + pyrite (Py-III) + galena + sphalerite + minor chalcopyrite. The bulk of the molybdenite was deposited in Stage II. In situ S isotope analyses of the sulfide ores show that the S34S values vary from -5.2 to +7.8%o (mean = +2.9%o) and correspond to S34SH2S values from -2.4 to +3.3%o (mean = +1.1%o). These values are consistent with a magmatic source for the sulfur. In situ Pb isotope compositions of the sulfide ores are almost identical to those of the local Mesozoic granites and other magmatic-hydrothermal ore deposits in this region, suggesting a close genetic association between the Mo mineralization and felsic magmatism. Pyrite from the three stages of mineralization differs significantly in its trace element composition. The first generation, Py-I, has a high Cu content (8.7 ± 49.6 ppm; where the first value is the median and the second is the standard deviation) and Mo content (6.9 ± 3.8 ppm). Pyrite-II has the lowest Cu concentration (1.3 ± 2.1 ppm) and a relatively high Mo concentration (5 ± 128 ppm), and Py-III has a high Cu content (8.7 ± 37.1 ppm) but the lowest Mo content (0.05 ± 5.7 ppm). From this, we infer that pyrite recorded the chemical evolution in the Mo/Cu ratio of the ore fluid and that this ratio reached a maximum in Stage II, coinciding with the widespread saturation of the fluid in molybdenite. The evolution of the Mo/Cu ratio in pyrite implies that the fluid was undersaturated in chalcopyrite at the high temperature of Stage I, despite the Cu concentration of the fluid apparently being at its high level, and chalcopyrite only saturated later, at a lower temperature. Molybdenite, however, because of its lower solubility, saturated early (Stage I) and in the subsequent stage (Stage II) was supersaturated in the fluid. There is a significant enrichment of Mo in the syn-ore intrusions at Chalukou compared to the pre-ore monzogranite. The very low Sr/Y ratios for the Chalukou syn-ore intrusions, which are in sharp contrast to the high Sr/Y ratios of the pre-ore monzogranite and those of porphyries related to Cu deposits, suggest that fractional crystallization of plagioclase may have been a key factor in generating the syn-ore magmas. Molybdenum is a highly incompatible metal and will concentrate in the crust, and assimilation of old continental crust, therefore, may explain the Mo enrichment of the syn-ore intrusions and ultimately the formation of the giant Chalukou deposit. [ABSTRACT FROM AUTHOR]

The 11.6 to 9.5 Ma Serifos pluton intruded schists and marbles of the Cycladic Blueschist unit, causing thermal metamorphism, the development of magnetite Ca-exo- and endo-skarns and the formation of low-temperature vein and carbonate-replacement ores. Potentially, the most important ores occur in the Moutoulas prospect where the mineralization in retrograde skarn and quartz veins culminated with the deposition of native bismuth. A combination of fluid inclusion microthermometry and isotope geothermometry suggests that the Moutoulas mineralization formed at a hydrostatic pressure of ~100 bars, from moderate-to-low temperature (~190-250 °C), and low-salinity (1.3-5.6 wt% NaCl equivalent) fluids. The calculated δ34SH2S compositions are consistent with the ore fluids having been derived from the Serifos pluton. Bismuth mineralization is interpreted to have occurred as a result of wall-rock interaction and mixing of a Bi-bearing ore fluid with meteoric waters. Native bismuth and bismuthinite deposited at ~200 °C, near neutral pH (6.5), low fS2 (<-16.5), and low fO2(<-44). Supergene alteration in Serifos led to the oxidation of native bismuth to bismite and bismutite. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the kinetic controls on serpentine crystallization using a flow-through autoclave. Experimental and analytical methods; Composition of the fluid; Investigation of serpentine morphology using transmission electron microscopy; Conclusions.

Presents a study on the composition and structural state of columbite-tantalite rocks located in rare-element granitic pegmatites from the Preissac-Lacorne batholith, Quebec, Canada. Experimental procedure; Characteristics of pegmatites; Types of pegmatites; Nomenclature.

Reexamines the genesis of zirconosilicates like elpidite, armsrongite and gittinsite at the Strange Lake pluton, Quebec-Labrador, Canada in light of textural and mineral chemical data collected from representative diamond-drill hole (DDH). Geological setting; Geology of DDH SL-182; Distribution of zirconosilicate minerals in DDH SL-182.