The vein-type tungsten deposit at Nyakabingo in the central Tungsten belt of Rwanda is located in the eastern flank of the complex Bumbogo anticlinal structure. The host rock is composed of alternating sequences of sandstones, quartzites, and black pyritiferous metapelitic rocks. Two types of W-mineralized quartz veins have been observed: bedding-parallel and quartz veins that are at high angle to the bedding, which are termed crosscutting veins. Both vein types have been interpreted to have been formed in a late stage of a compressional deformation event. Both vein types are associated with small alteration zones, comprising silicification, tourmalinization, and muscovitization. Dating of muscovite crystals at the border of the veins resulted in a maximum age of 992.4 ± 1.5 Ma. This age is within error similar to the ages obtained for the specialized G4 granites (i.e., 986 ± 10 Ma). The W-bearing minerals formed during two different phases. The first phase is characterized by scheelite and massive wolframite, while the second phase is formed by ferberite pseudomorphs after scheelite. These minerals occur late in the evolution of the massive quartz veins, sometimes even in fractures that crosscut the veins. The ore minerals precipitated from a H2O–CO2–CH4–N2–NaCl–(KCl) fluid with low to moderate salinity (0.6–13.8 eq. wt% NaCl), and minimal trapping temperatures between 247 and 344 °C. The quartz veins have been crosscut by sulfide-rich veins. Based on the similar setting, mineralogy, stable isotope, and fluid composition, it is considered that both types of W-mineralized quartz veins formed during the same mineralizing event. Given the overlap in age between the G4 granites and the mineralized quartz veins, and the typical association of the W deposits in Rwanda, but also worldwide, with granite intrusions, W originated from the geochemically specialized G4 granites. Intense water–rock interaction and mixing with metamorphic fluids largely overprinted the original magmatic-hydrothermal signature.
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RBINS Staff Publications 2016
The hog deer (Axis porcinus) is an endangered cervid with drastic population declines. There are 2 recognized subspecies of hog deer: A. p. porcinus, ranging from Punjab Province in Pakistan, Nepal, and the Northern part of India to Myanmar, and A. p. annamiticus found in Indo-China, Thailand, Laos, Cambodia, and Vietnam. The current geographic range of A. p. annamiticus is still ambiguous. We analyzed variation in the mitochondrial DNA control region (mtDNA CR) to investigate the intra-species structure, differentiation, and demographic history of hog deer from Cambodia (Kratie Province), which we compared with the populations from India and Thailand. We also generated divergence time estimates using a concatenated dataset of complete Cyt b and partial CR. The CR data showed that Cambodian hog deer are genetically differentiated from the mainland Indian and Thai populations, forming a distinct basal clade. The time of divergence indicates that the Cambodian lineage split from the other 2 hog deer lineages around 0.51 Mya, during the Late Pleistocene. The results also suggest strong phylogeographic structure among hog deer: lineage A extends from Terai Arc (foothills of the Himalayas) to Assam, India (A. p. porcinus), lineage B from Manipur, India to Thailand (A. p. annamiticus), and lineage C is only known from Kratie Province, Cambodia. Lineage A exhibited a higher level of genetic diversity than lineages B and C, with recent demographic stability. Thus, the hog deer population in Kratie Province appears to be a distinct lineage that should be treated as an evolutionarily significant unit.
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RBINS Staff Publications 2022
