Abstract
Major trace element analyses, including pyrite chemistry of pyritic mudstones of shallow-marine Singa Formation of Pennsylvanian–Early Permian age have been carried out to assess gold potential, the source of sulfur and organic matter. Regionally, Singa Formation spatially correlates with the Bohorok Formation (Sumatra, Indonesia), the Kaeng Krachang group (Thailand), and the Lebyin group (Burma or Myanmar). In Southeast Asia, this formation is important because it has a record of glacial processes that occurred along the northern margin of Gondwana in the Late Paleozoic age. This study has revealed that mudstones of the Singa Formation, which contain lonestones of glacial origin, deposited under suboxic–oxic conditions in shallow marine environment during Pennsylvanian–Early Permian time. The black mudstones contain total organic carbon which ranges from 0.1 to 0.7 wt.%, and gold content varying from 40 to 62 ppb, making them gold source rocks. This study has revealed diagenetic gold presence in the early pyrite generations (pyrites 1, 2, and 3) in these mudstones with gold content ranging up to 1.6 ppm Au which is indicative of early enrichment of gold. Conversely, late generations of pyrite (pyrites 4, 5, and 6) in these mudstones record low gold content up to 0.5 ppm Au. The δ34S values for pyrite grains range from −24.6‰ to +6.2‰ likely indicate a combination of magmatic and biogenic source of sulfur. Organic carbon isotope composition of the pebbly mudstone samples shows a wide range from −23.9‰ to −5.8‰ indicating a mixed terrestrial and marine source.
Highlights
Fine-grained sedimentary sequences host several trace elements, including Zn, Pb, Cu, Mo, Se, V, U, Ni, As, Ag, Sb, Cr, and Au [1,2,3,4]
Black shales are host to significant gold deposits in certain regions in the world such as the Chuniespoort Group of the Late Archean–Early Proterozoic Transvaal Sequence (South Africa), the Central Gold Belt (Malaysia), and the Sepon Mineral District (Laos), the Mathinna Turbidite deformed sequence in Northeast Tasmania (Australia), Upper Devonian black shale series of the Xikuangshan Sb deposit in Hunan (China) [5,6,7,8,9]
The results indicate that gold content from the black mudstones, varying up to 62 ppb, is well above the worldwide dataset
Summary
Fine-grained sedimentary sequences host several trace elements, including Zn, Pb, Cu, Mo, Se, V, U, Ni, As, Ag, Sb, Cr, and Au [1,2,3,4]. Black shales (commonly metamorphosed to greenschist facies) are host to significant gold deposits in certain regions in the world such as the Chuniespoort Group of the Late Archean–Early Proterozoic Transvaal Sequence (South Africa), the Central Gold Belt (Malaysia), and the Sepon Mineral District (Laos), the Mathinna Turbidite deformed sequence in Northeast Tasmania (Australia), Upper Devonian black shale series of the Xikuangshan Sb deposit in Hunan (China) [5,6,7,8,9]. Tasmania (Australia), Upper Devonian black shale series of the Xikuangshan Sb deposit in Hunan (China) [5,6,7,8,9]. Knowing the origin and isotopic signature of the organic carbon and sulfur is important as mudstones or shales in orogenic gold systems often have el2evated.
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