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Two types of turquoise, including homogeneous Cu-rich turquoise and oscillatory zoned turquoiseplanerite series, are recognized in association with quartz-barite veins hosted by Cambrian carbonaceous slates from western Hubei Province of China. Combined fluid inclusion and Raman micro-spectroscopic data reveal that turquoise-bearing barite-quartz veins contain three types of fluid inclusions (pure CH4-N2, carbonic-aqueous, and aqueous), suggesting the responsible fluid is of carbonic-aqueous composition with low oxygen fugacity. Pressure-corrected homogenization temperatures in quartz and barite show a range from 325 to 485 °C and 186 to 391 °C, respectively. Carbon, oxygen, and hydrogen isotopic data suggest that the mineral-forming fluids have a mixed metamorphic-organic affinity, in which the fluids have δ18O and δD values of 15.0 to 18.8‰ and –111 to –93‰, respectively. Generally, the formation of quartz-barite-turquoise veins could be triggered by prior metamorphic devolatilization, followed by the interaction of fluids with country rocks enriched in carbonaceous material, which resulted in the leaching of Cu, Fe, P, and Al from chalcopyrite, pyrite, magnetite, monazite, xenotime, apatite, feldspar, and muscovite in the wall rocks. Decomposition of the organic matter in the carbonaceous slates, caused by regional metamorphism and deformation, could also promote the concentration and transportation of necessary metals for the turquoise. Thus, we propose a new model and suggest that the turquoise gem deposits in western Hubei Province of China belong to the non-magmatic hydrothermal vein type deposit, not the previously proposed supergene origin. The turquoise-forming fluids were characterized by the coexistence of two immiscible fluids of non-magmatic affinity (i.e., moderate to high-temperature and low-salinity aqueous fluid and pure CH4-N2 fluid formed by interaction with carbonaceous slates). The bluish green homogeneous turquoise in the metamorphic quartz-barite-turquoise veins evolved toward the turquoise-planerite solid solution series as the metal-leaching capability of the aqueous fluids decreased. [ABSTRACT FROM AUTHOR]

The Hongqiling magmatic Ni-Cu sulfide deposit, situated on the southern margin of the eastern Central Asian Orogenic Belt (CAOB), is composed of over 30 mafic-ultramafic intrusions. These ore-bearing intrusions are composed mainly of harzburgite, lherzolite, websterite, orthopyroxenite, and norite (gabbro). The constituent minerals are olivine, diopside, bronzite, calcic-hornblende, plagioclase, and spinel with orthopyroxene as a dominant mineral in these intrusions. These ore-bearing intrusions are not Alaskan-type complexes. Spinel and clinopyroxene both exhibit different chemical compositions from those in the Alaskan-type complexes. The rocks that make up the intrusions have high contents of MgO (average value = 25.20 wt.%) and low Ti[O.sub.2] (average value = 0.58 wt.%). The high MgO contents of the minerals and the high Mg (#) (71) of the calculated melt in equilibrium with olivine demonstrate that the parental magma of the Hongqiling mafic-ultramafic intrusions was a high-Mg tholeiitic magma. The Hongqiling ore-bearing mafic-ultramafic intrusions and the calculated 'trapped liquids' for the olivine-orthopyroxene cumulate rocks are all enriched in large-ion lithophile elements and depleted in high field strength elements. The Ce/Pb, Ta/La, Th/Yb, and (La/Sm)PM values and the depletion of Nb and Ta suggest that the magma experienced crustal contamination. The Hongqiling ore-bearing intrusions display many similarities with mafic-ultramafic intrusions that formed in a post-collisional extensional environment in the western CAOB (e.g., Huangshanxi). Common features include their whole-rock compositions and mineral chemistry. Combined with the evolutionary history of the eastern segment of the CAOB, we believe that the Late Triassic Hongqiling mafic-ultramafic intrusions formed in a post-collisional extensional environment.Le gisement magmatique de sulfures a Ni-Cu de Hongqiling, situe a la bordure sud de la ceinture orogenique d'Asie centrale (COAC), renferme plus de 30 intrusions mafiques-ultramafiques. Ces intrusions mineralisees sont constituees principalement d'harzburgite, de lherzolite, de websterite, d'orthopyroxenite et de norite (gabbro). Les mineraux constituants sont l'olivine, le diopside, la bronzite, la hornblende calcique, le plagioclase et le spinelle, l'orthopyroxene etant un mineral dominant dans ces intrusions. Ces intrusions mineralisees ne sont pas des complexes de type alaskien. Le spinelle et le clinopyroxene presentent tous deux des compositions chimiques differentes de celles de complexes de type alaskien. Les roches qui composent les intrusions ont de fortes teneurs en MgO (moyenne = 25,20% en poids) et de faibles teneurs en Ti[O.sub.2] (moyenne = 0,58% en poids). Les fortes teneurs en MgO des mineraux et le Mg (#) eleve (71) de la composition calculee du magma en equilibre avec l'olivine demontrent que le magma parental des intrusions mafiques-ultramafiques de Hongqiling etait un magma tholeiitique riche en Mg. Ces intrusions et les [much less than]liquides pieges[much greater than] qui ont produit les cumulats a olivine et orthopyroxene sont tous enrichis en elements lithophiles a grand rayon ionique et appauvris en elements a forte liaison atomique. Les valeurs de Ce/Pb, Ta/La, Th/Yb et (La/Sm)PM et l'appauvrissement en Nb et Ta donnent a penser que le magma a subi une contamination crustale. Les intrusions mineralisees de Hongqiling partagent de nombreuses similitudes avec les intrusions mafiques-ultramafiques formees dans un milieu d'extension post-collision dans la partie ouest de la COAC (p. ex. Huangshanxi), dont leurs compositions sur roche totale et la chimie de leurs mineraux. La combinaison de ces resultats et de l'evolution du segment est de la COAC nous porte a croire que les intrusions mafiques-ultramafiques de Hongqiling du Trias tardif se sont formees dans un milieu d'extension post-collision. [Traduit par la Redaction], IntroductionA number of small Ni-Cu ore-bearing mafic-ultramafic intrusions occur in the southern part of the Central Asian Orogenic Belt (CAOB); examples include the Kalatongke (Song and Li 2009; Z.C. Zhang [...]

Geothermal systems in Tibet, a crucial geothermal region in China, belong to the Mediterranean-Himalayan geothermal belt and are characterized by a broad distribution of cesium (Cs) bearing geyserite deposits. Targejia, one of the largest Cs-bearing geyserites in southern-western Tibet, contains 1.446 × 104 tons of Cs. The highest ore grade reaches 2.89 wt%, and the ore-forming process can be subdivided into mineralization stages I to V. Cs is heterogeneously distributed in geyserites. Herein, two Cs-bearing ores are investigated, with distinct characteristics of (1) low-Cs-bearing ore (amorphous silica opal-A and opal-CT type) with low Cs (average of ~0.2 wt%), Na, K, Al, and Ca contents, and (2) high-Cs-bearing ore (clay type) with high-Cs (average of ~1.40 wt%), -Na, -K, -Al, and -Ca contents. It is reported for the first time that Cs primarily exists in clay rather than in amorphous silica opal. The Cs-enrichment mechanisms are diferent for the above two Cs-bearing geyserite types: (1) The deprotonated –OH, surrounded by water molecules, controls the amount of Cs absorbed on the geyserite surface (Si–OH) in the low-Cs-bearing ore. (2) The variable Cs content depends on the Al content because Al substitutes Si, yielding more negative charges to absorb Cs in the high-Cs-bearing ore. Geothermal fluid loading-mass elements, such as Cs and SiO2, precipitate as amorphous silica (opal) with clay minerals. Mineral saturation index modeling was used to predict the most applicable physical parameters for ore formation. The results confirm that the ore forms at ~85 °C and a pH of ~8.5 in the Na-Cl system at stage V. The degree of Cs enrichment reduces from the latest stage V (0–4 ka) to the early stage IV (4–17 ka), and is controlled by clay dissolution, which might further relate to the climate change in Tibet's Holocene. Fluid-rock interaction modeling shows that dissolution–reprecipitation induces a higher order of amorphous silica formation and clay dissolution at >40 °C and pH of 5–9 at stages V and III, excluding Cs from the ore. [ABSTRACT FROM AUTHOR]