The relationship between hydrocarbon accumulation and Mississippi Valley‐type Pb‐Zn mineralization of the Mayuan metallogenic belt, the northern Yangtze block, SW China: Evidence from ore geology and Rb‐Sr isotopic dating

Abstract

The coexistence of Pb‐Zn deposits and oil/gas reservoirs demonstrates that a close genetic connection exists between them. The spatiotemporal relationship between Pb‐Zn mineralization and hydrocarbon accumulation is the key to understanding this genetic connection. The Mayuan large‐scale Pb‐Zn metallogenic belt is composed of a number of Mississippi Valley‐type (MVT) Pb‐Zn deposits that were recently discovered on the northern margin of the Yangtze Block, China. It is hosted in the dolostone of the Sinian (Ediacaran) Dengying Formation (Z2dn). In addition to the abundant bitumen in the Mayuan Pb‐Zn metallogenic belt, the paleo‐oil reservoir and the MVT Pb‐Zn deposit overlap in space. In this study, two precise ages of 468.3 ± 3.8 Ma and 206.0 ± 6.5 Ma were obtained via the Rb‐Sr isotopic dating of galena and sphalerite from the Mayuan Pb‐Zn metallogenic belt, respectively. The early metallogenic age of 468.3 ± 3.8 Ma is similar to the previously published age of 486 ± 12 Ma. The age of 206.0 ± 6.5 Ma is consistent with the age of the metallogenic event that occurred at 200 Ma in the Upper Yangtze Pb–Zn metallogenic province of the Sichuan‐Yunnan‐Guizhou polymetallic zone, which is located on the southwest margin of the Sichuan Basin, suggesting that the metallogenic effects of this period were regional in scale in the peripheral areas of the Sichuan Basin. Previous studies have shown that two periods of hydrocarbon accumulation occurred in the oil/gas reservoir that coexists with the Pb‐Zn deposits in the study area. The Pb‐Zn mineralization at 468.3 ± 3.8 Ma occurred during the first period of hydrocarbon accumulation, while the second mineralization at 206.0 ± 6.5 Ma occurred during the transformation of the paleo‐oil reservoir to a paleogas reservoir. The spatial relationship between the paleo‐oil/‐gas reservoir and the MVT Pb‐Zn deposits and the temporal relationship between mineralization and hydrocarbon accumulation show that a close genetic relationship exists between the MVT Pb‐Zn mineralization and hydrocarbon accumulation. Analysis of metals in the source rocks forming the paleo‐oil/‐gas reservoirs show that source rocks which formed paleo‐oil/‐gas reservoirs may have provided metals for Pb‐Zn mineralization. Both the paleo‐oil/‐gas reservoirs and Pb‐Zn mineralizing fluids had the same origin.

Genetic Relationship between Mississippi Valley-Type Pb–Zn Mineralization and Hydrocarbon Accumulation in the Wusihe Deposits, Southwestern Margin of the Sichuan Basin, China

“…The Cambrian-middle Permian and lower Permian strata mainly consist of carbonate-clastic rock deposits and continental basalt, respectively [31][32][33]. The Ediacaran Dengying Formation is not only the main host of MVT Pb-Zn deposits [7,8,30,36,[38][39][40] but also an important commercially productive source of natural gas in the Sichuan Basin [41][42][43][44]. Many MVT Pb-Zn deposits have been found in the relict paleo-oil/gas reservoirs in the Dengying Formation located in the periphery of the Sichuan Basin [7,8,45]; the Wusihe Pb-Zn deposits located in the southwestern margin of the Sichuan Basin is one representative example of these deposits.…”

“…The Ediacaran Dengying Formation is not only the main host of MVT Pb-Zn deposits [7,8,30,36,[38][39][40] but also an important commercially productive source of natural gas in the Sichuan Basin [41][42][43][44]. Many MVT Pb-Zn deposits have been found in the relict paleo-oil/gas reservoirs in the Dengying Formation located in the periphery of the Sichuan Basin [7,8,45]; the Wusihe Pb-Zn deposits located in the southwestern margin of the Sichuan Basin is one representative example of these deposits. The gas reservoirs in the Dengying Formation, such as the Gaoshiti and Moxi gas reservoirs, are mainly distributed in the deeply buried traps located in the central Sichuan Basin [41][42][43][44], and sporadic sphalerite and galena can be observed in these commercially productive natural gas reservoirs.…”

“…Mississippi Valley-type (MVT) zinc-lead (Zn-Pb) deposits are carbonate-hosted epigenetic stratabound deposits and are believed to form from basinal brines [1]. Numerous MVT Pb-Zn deposits show special spatiotemporal associated or paragenetic relationships and genetic links with paleo-oil reservoirs [1][2][3][4][5][6][7][8]. Bitumen, as a common byproduct of hydrocarbon formation, is direct evidence of the existence of oil/gas reservoirs in these deposits.…”

“…Therefore, the oil and metal-organic complexes in oil are transported and accumulate together, and the destruction of oil reservoirs or gas reservoirs results in mineralization. Mineralization in certain MVT Pb-Zn deposits have been attributed to this genetic model [7,8,27,28].…”

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

“…Sedimentary basin is a huge complex system in which a variety of organic and inorganic, metallic and nonmetallic mineral resources and water resources coexist [1]. As the phenomenon of close paragenesis or associated occurrence between metal deposits and hydrocarbon organic matter has been discovered [2][3][4][5][6][7][8][9][10][11][12], the relationship between metal mineralization and hydrocarbon accumulation has attracted more and more attention of mineral deposit scholars, and the study of organic-inorganic interaction and mineralization effect in sedimentary basins has been aroused [13][14][15][16][17][18].…”