Petroleum geology
Nasim Maleki Sadeghi; Ahmad Ahmadi-khalaji; Reza Zarei Sahamieh; Zahra Tahmasbi
Abstract
The study area is a part of Zagros Folded zone and located in the Lorestan sedimentary basin. In this regard, three areas with high bitumen potential were selected, which include the northern area of Kuhdasht, northeast of Poldokhtar and southeast of Sepiddasht. In the study areas, bitumens are exposed ...
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The study area is a part of Zagros Folded zone and located in the Lorestan sedimentary basin. In this regard, three areas with high bitumen potential were selected, which include the northern area of Kuhdasht, northeast of Poldokhtar and southeast of Sepiddasht. In the study areas, bitumens are exposed as veins between the fractures and as interlayers with host rock that the thickness of these veins is between 10 cm to more than 1.5 meters. Field studies showed that the studied bitumens have developed in the shales of Amiran Formation. Based on the results of organic geochemistry, 80.10 to 93.60% of the extractable saturated compounds are in the category of asphalts and have a very good quality in terms of thermal maturity (maturity of organic matter). The studied samples are formed in a reducing to slightly reducing sedimentary environment. Drawing the diagram of C34/C35 Homohopane vs. C29/C30 Hopane for the studied bitumens showed that the generating rocks of the studied samples are carbonate and detrital in nature. This can be explained by the lithology of bituminous formations such as Ilam and Gurpi formations in the study areas. The triangular diagram of regular streams (m/z = 217) for the studied bitumens showed that the source of organic compounds of the studied bitumens is mostly marine with a small amount of entry from dry environments. Severe depletion of the carbon isotope (average -28.83 per mill) indicates organic origin and biomass in these samples. On the other hand, sulfur compounds with depletion (-12.16 per mill) indicate formation in a reduced to semi-regenerated sedimentary environment and oxygen isotope data (+15.03 per mill) indicate the formation of organic matter of sedimentary origin.
E. Ashrafpour; K. M. Ansdell; S. Alirezaei
Abstract
Arghash gold district includes five gold-bearing vein systems, (Au-ItoAu-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-ItoPy-IV). Py-I toIII are intimately ...
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Arghash gold district includes five gold-bearing vein systems, (Au-ItoAu-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-ItoPy-IV). Py-I toIII are intimately associated with gold; however, Py-IV is barren. The δ34S values of pyrites in conventional bulk analyses fall into two groups, one highly enriched in 34S (δ34S= +9.3 to +21.8‰), and the other less enriched to slightly depleted in 34S (δ34S= +5.1 to -4.3‰). In-situ laser probe experiments were carried out to characterize various generations of pyrite. The results indicate a relatively narrow range for Py-I to Py-III (δ34S= -5.8 to +0.1‰) consistent with a magmatic source for sulfur. Py-IV is highly enriched (δ34S= +8.9 to +23.7‰), implying contributions of sulfur from sources enriched in 34S, like evaporites. The high δ34S values in the enriched group can be attributed to a significant occurrence of Py-IV in this group.
The δ34S values of two stibnites from Sb ore (-18.8 and -14.4‰) suggest a different sulfur, and possibly metal source, and/or radical changes in the physicochemical conditions of the fluid during deposition of stibnite. Metasedimentary basement rocks could contribute sulfur and metal to the circulating fluids. δ13CPDB values of vein calcites are near 1 per mil suggesting a sedimentary source for carbon. Carbonate units and interlayers in the area are a suitable source for CO2 in the ore fluids. The stable isotope data suggest that hydrothermal fluids experienced a complex history of water/rock interaction and that ore components, were derived, at least partly, from country rocks.
