Re–Os Dating of Bitumen from Paleo–Oil Reservoir in the Qinglong Antimony Deposit, Guizhou Province, China and Its Geological Significance

Abstract

Abundant organic inclusions are present in the Qinglong antimony deposit. However, the source rocks of these organic matters have not been reliably identified. Recently, a paleo‐oil reservoir was found in the Qinglong antimony deposit. In view of similar components of gaseous hydrocarbon, we propose that the organic matters observed in inclusions in Qinglong antimony deposit would come from this paleo‐oil reservoir. We used the Re‐Os dating method to determine the age of the bitumen from this paleo‐oil reservoir, and obtained an isochron age of 254.3±2.8 Ma. The age indicates that the oil‐generation from source rock occurred in the early Late Permian, earlier than the Sb mineralization age (∼148±8.5 Ma) in the Qinglong antimony deposit area. After oil generation from Devonian source rock, first and secondary migration, the crude oil have probably entered into the fractures and pores of volcanic rocks and limestone and formed a paleo‐oil reservoir in the western wing of Dachang anticline. As burial process deepened, the crude oil has turned into natural gas, migrates into the core of Dachang anticline and formed a paleo‐gas reservoir. The hydrocarbons (including CH4) in the reservoirs can serve as reducing agent to provide the sulfur required for Sb mineralization through thermal chemical reduction of sulfates. Therefore, the formation of oil‐gas in the area is a prerequisite for the Sb mineralization in the Qinglong antimony deposit.

TSR Action and Genesis Mechanism of Antimony Deposit: Evidence From Aromatic Hydrocarbon Geochemistry of Bitumen in Paleo-Oil Reservoir Near Qinglong Ore Field, Southwestern Guizhou Depression, China

“…Au-Sb deposits occur mainly in the Permian to Middle Triassic impure carbonate rocks and terrigenous fine clastic rocks, and often coexist with or adjacent to paleo-oil reservoirs, remnant oil and gas, and bitumen in the Permian reef and shoal carbonate rocks in space (Figure 1). The host rocks and ores of these deposits are characterized by rich organic matter, and the hydrothermal minerals of the ore often contain rich bitumen and hydrocarbon organic inclusions, indicating a close genetic relationship between gold and antimony mineralization and oil and gas accumulation [9,38].…”

“…The Triassic is carbonate rock and clastic rock (Figure 2). The strata exposed in Qinglong antimony ore field are mainly Permian, including middle Permian Maokou Formation limestone (P2m), "Danchang layer" (P3d), Upper Permian Emeishan basalts (P3β) and Upper Permian Longtan Formation coal-bearing strata (P3l) from old to new [38] (Figure 3). The ore field is obviously controlled by NE-striking structure.…”

“…As a reducing agent, the organic matter of oil and gas produces a large amount of reduced sulfur through TSR reaction, which is the only way to form high concentration H2S oil and gas reservoirs. TSR reaction is also an important formation mechanism of reduced sulfur in many metal deposits [6,38,[97][98]. TSR total reaction equation is as follows:…”

“…Fortunately, in 2012, our team found a paleo-oil reservoir in the Shailing ore block when we were prospecting outside the Qinglong antimony deposit [36][37], which created conditions for further discussion on the relationship between organic matter and antimony mineralization. Our team has carried out some research work on paleo-oil reservoir bitumen, including physical characteristics and genesis of bitumen, element geochemistry, organic geochemistry, S-C isotope, inclusion, Re-Os isotope dating and its relationship with antimony deposit [36][37][38][39][40]. Based on the data, we believe that hydrocarbon organic matter is involved in antimony mineralization and contributes a large amount of reduced sulfur to antimony mineralization through thermochemical sulfate reduction (TSR) reaction [38][39][40].…”

“…Our team has carried out some research work on paleo-oil reservoir bitumen, including physical characteristics and genesis of bitumen, element geochemistry, organic geochemistry, S-C isotope, inclusion, Re-Os isotope dating and its relationship with antimony deposit [36][37][38][39][40]. Based on the data, we believe that hydrocarbon organic matter is involved in antimony mineralization and contributes a large amount of reduced sulfur to antimony mineralization through thermochemical sulfate reduction (TSR) reaction [38][39][40].…”