Fluid Inclusions and Isotope Geochemistry of the Emba Derho and the Debarwa VMS Deposits, Asmara District, Eritrea

Objective Recent exploration indicates several localities with significant gold, copper, and zinc resource potential in the Asmara district, Eritrea, including the Emba Derho and Debarwa volcanic-associated massive sulfide deposits. These deposits are hosted by the Neoproterozoic metamorphic volcanic rocks of Asmara green stone belt, which strike NNW-SSE and are 200 km long and 5-20 km wide, and the mineralization is often associated with the altered and deformed rocks. The Emba Derho deposit, located 12 km northwest of Asmara （Fig. la）, the capital of Eritrea, is the largest Cu-Zn-Au VMS deposit in the Asmara metallogeny belt. It is estimated that the Emba Derho deposit of the Asmara project contains total reserves of 49.8~106 tons of copper ores and 16.8~106 tons of zinc ores. The gold grade of this deposit is about 0.3 lg/t. The Debarwa deposit, situated 26 km southwest of Asmara, has similar ore features with the Emba Derho deposit.

Fluid Inclusion and Stable Isotope Geochemistry of the Shangxu Gold Deposit, Northern Tibet

Objective The Shangxu gold deposit is located in the south of the middle Bangong-Nujiang suture zone in northern Tibet. The origin of this deposit as an orogenic gold deposit is debatable. The study of the Shangxu deposit has a profound implication on gold exploration in the Bangong- Nujiang metallogenic belt and can also improve our understanding of gold mineralization in northern Tibet.

Fluid Inclusion and Geochemistry Studies of Calcite Veins in Shizhu Synclinorium,Central China:Record of Origin of Fluids and Diagenetic Conditions

Calcite veins in carbonate fracture have been investigated by petrographic, fluid inclusion, geochemical analyses and coupled with basin modeling techniques to provide useful insights into fluid activity and deformation conditions of the Cambrian to Triassic Shizhu synclinorium from the western region of Mid-Yangtze, central China. The results of the fluid inclusion microthermometry show a wide range of homogenization temperatures（78.6–215.5 °C） and salinities（0.18–23.11 wt.% NaCl equivalent）, indicating the formation under diverse fluid conditions. All the calcite veins have negative Ce anomalies, which are the typical characteristic of marine carbonate sediments; it is therefore plausible that calcite veins were precipitated from the marine basin fluid. The stable carbon isotopic compositions of calcites（δ^（13）CV-PDB=-2.5‰–4.26‰） and host limestones（δ^（13）CV-PDB=-3.56‰–5.80‰） are very similar with a correlation coefficient of 0.86, however, four calcites from the Lower Permian and Lower Triassic show lower δ^（13）C values relative to the host limestones, and they are depleted in total REE concentrations（∑REE ratio varies from 0.74 to 2.06）, suggesting the derivation of dissolved carbon from marine carbonates hosting the calcite veins and, less commonly, from the degradation of organic matter. Calculated δ^（18）O of the fluids-precipitating calcites（δ^（18）OV-SMOW=-0.41‰–14.42‰）, ^（87）Sr/^（86）Sr ratios varying in the range of coeval seawater and the distinct REE pattern simultaneously suggest calcite-forming fluids in each stratigraphic unit could have formed from the involvement of fluids that originated from coeval seawater and evolved through different degrees of water rock interaction. However, the presence of more radiogenic ^（87）Sr/^（86）Sr ratios than coeval seawater and pronounced positive Eu anomalies in calcites of Lower to Middle Ordovician rocks indicate that terrestrial input from upper strata mudstone and siliciclastic rocks could be involved in the precipitation of the Ordovician calcite. Fluid-inclusion data combined with burial and thermal history modeling indicate there was large-scale flow of evolved basinal fluids through the carbonate formation fractures spanning a time frame from 135 to 50 Ma（Early Cretaceous–Eocene）. Therefore, the geochemical characteristics of calcite veins can provide the basis for deformation events in Late Yanshanian and Early Himalayan orogeny.