The Xietongmen district is located 260 km west-southwest of Lhasa in the Tibet Autonomous Region, China. The district occurs within the Gangdese belt, which forms the eastern part of the Trans-Himalayan magmatic belt and is the product of complex magmatic activity that began during the Late Triassic or Early Jurassic and ended in the Eocene. The Xietongmen Cu-Au and Newtongmen Cu-Au-Mo deposits contain a total measured and indicated resource of approximately 610 million metric tons, with additional mineralization in the Langtongmen and Olitongmen Cu-Au prospects. Porphyry mineralization in the Xietongmen district formed during Middle Jurassic volcanic arc activity in the Lhasa terrane, prior to its accretion to the southern margin of Eurasia, and establishes that an economically important, but only recently recognized, metallogenic event is present in the region.Rock types in the Xietongmen district range from Early Jurassic to Eocene in age. Early Jurassic (~188−177 Ma) volcanic, volcaniclastic, and coeval intrusive rock types are crosscut by Middle Jurassic (176−171 Ma) hornblende diorite and quartz diorite porphyry dikes and stocks, including intrusions related to porphyry Cu-Au ± Mo mineralization. The Jurassic igneous assemblage was intruded by mafic dikes between the Late Jurassic and the Cretaceous, then by an Eocene (50−47 Ma) biotite granodiorite batholith and related dikes, and finally by, volumetrically minor lamprophyre dikes. The most important structures in the Xietongmen district are four E-striking, moderately N-dipping, sinistral-oblique thrust faults. Crosscutting and suturing relationships between the TSF-2 thrust fault, located in the south part of the district, and intrusions dated to between 174 and 180 Ma constrain the main stage of thrust fault activity to the Middle Jurassic. The Contact and Adit-1 thrust faults truncate the Xietongmen deposit and form the footwall and hanging wall to mineralization, respectively. Numerous zones of cataclasis deform the Xietongmen deposit between these bounding thrust surfaces. The strongly deformed Langtongmen Cu-Au prospect is located ~1.3 km west of the Xietongmen deposit and occurs in the immediate hanging wall of the Adit-1 thrust fault. The Newtongmen deposit and the Olitongmen Cu-Au prospect occur to the north in the hanging wall to the SBF thrust fault and are not strongly deformed.Mineralization and hydrothermal features in the Xietongmen district are fully compatible with porphyry Cu-Au ± Mo deposits. Alteration, vein types, and mineralization are zoned around quartz diorite porphyry intrusions. Early K silicate alteration and related veins occur within and proximal to the intrusions and contain the highest grade mineralization. In the Xietongmen deposit, the grade of mineralization decreases outward from a core of early biotite-rich K silicate alteration, through a transitional zone in which early K silicate alteration is partially overprinted by quartz-sericite-pyrite alteration, to a peripheral zone of poorly mineralized quartz-sericite-pyrit...
Temperature and dissolved oxygen concentrations were measured monthly from January 1971 to December 1982 at 1-rn depth intervals at 13 stations in Keowee Reservoir in order to characterize spatial and temporal changes associated with operation of the Oconee Nuclear Station. The reservoir water column was ito 4°C warmer in operational than in non-operational years. The thermodine was at depths of 5 to 15 m before the operation of Oconee Nuclear Station, but was always below the upper level of the intake (20 m) after the station was in full operation; this suggests that pumping by the Oconee Nuclear Station had depleted all available cool hypolimnetic water to this depth. As a result summer water temperatures at depths greater than 10 rn were usually 10°C higher after plant operation began than before. By fall the reservoir was nearly homothemious to a depth of 27 m, where a thermocine developed. Seasonal temperature profiles varied with distance from the plant; a cool water plume was evident in spring and a warm water plume was present in the summer, fall, and winter. A cold water plume also developed in the northern section of the reservoir due to the operation of Jocassee Pumped Storage Station. Increases in the mean water temperature of the reservoir during operational periods were correlated with the generating output of the power plant. The annual heat load to the reservoir increased by one-third after plant operations began. The alteration of the thermal stratification of the receiving water during the summer also caused the dissolved oxygen to mix to greater depths. (
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