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[Display omitted] • The bitumen in wall rocks and the Danzhai paleo-oil reservoir both originate from the Lower Cambrian source rock. • The paleo-oil reservoir and the ore sulfur both derive from seawater sulfate in the strata. The metallogenic metals are mainly sourced from the underlying strata and basement. • Bitumen Re-Os and sphalerite Rb-Sr isotopes yield isochron ages of 424±160 Ma and 398±4.7 Ma, respectively. • Hydrocarbons supply a large amount of reduced sulfur for mineralization through TSR reaction. The Niujiaotang MVT Pb-Zn ore field is located at the southwestern end of the West Hunan-East Guizhou (WHEG) metallogenic belt, which overlaps spatially with the Majiang paleo-oil reservoir. The Pb-Zn mineralization is closely associated with oil-gas accumulation processes. However, the genetic link between the paleo-oil reservoir and the Pb-Zn deposits remains unclear. In this paper, we present new findings of bitumen (paleo-oil reservoir) and its features in the deposits, and apply various isotopic geochemical methods and 2D seismic data to elucidate the source rock and coupling relationship of the paleo-oil reservoir and the Pb-Zn deposits. This study reveals that the ore has a simple mineral composition, mainly comprising sphalerite, pyrite, and dolomite. Solid bitumen occurs widely in the ore and the host dolostone, and coexists with minerals from the mineralization stage. Laser Raman spectroscopy shows that the bitumen in the wall rocks of the Chengong deposit and the Danzhai paleo-oil reservoir are both overmature, and their carbon isotope compositions (δ13C PDB = –29.17 ‰ – –31.20 ‰, average –30.10 ‰, n = 6) and initial 187Os/188Os ratio (1.08±0.19) suggest that they have the Lower Cambrian source rock similar to the Majiang paleo-oil reservoir. The δ34S value of pyrite in the bitumen from the wall rocks in the Chengong deposit ranges from +28.15 ‰ to +44.12 ‰ (average +33.28 ‰, n = 18), which is consistent with the sulfur isotope composition of the ore sulfide reported previously, indicating that they both derived from sulfate in the Middle-Upper Cambrian strata. Bitumen Re-Os and sphalerite Rb-Sr isotopic dating indicate that oil reservoir accumulation in the ore-hosting strata preceded Pb-Zn mineralization, occurring at 424±160 Ma (MSWD = 1.3) and 398±4.7 Ma (MSWD = 0.66), respectively. The initial 87Sr/86Sr ratio of sphalerite is 0.709983±0.000027, which, after comparison and in combination with previous studies, suggests that the metallogenic metals mainly originated from the underlying strata and basement. 2D seismic data show that the Zaolou fault (F 2) that controls the mineralization is a deep fault that extends to the basin basement, and acts as a migration pathway for hydrocarbon fluids and ore-forming materials. We propose that liquid hydrocarbons played a significant role in Pb-Zn mineralization, acting as reductants to reduce sulfate through the thermochemical sulfate reduction (TSR) reaction and provide abundant reduced sulfur (H2S/HS−) for Pb-Zn mineralization. Finally, we present a comprehensive model of hydrocarbon accumulation and mineralization in the Niujiaotang ore field. [ABSTRACT FROM AUTHOR]

In recent years, China has made significant progress in exploring oil and gas in sandstone and carbonate rocks with burial depths of more than 6000 m in the Tarim, Sichuan, and Junggar Basins. These ultra-deep reservoirs have widely developed natural fractures that are important storage spaces and primary flow pathways influencing hydrocarbon enrichment and production. For ultra-deep tight sandstone, fractures caused by tectonic, diagenetic, tectonic-diagenetic, and overpressure processes are widespread. In the foreland thrust belt, which is divided into five fracture domains, fault-related folds affect fracture distribution in ultra-deep sandstones. For ultra-deep carbonate rocks, strike-slip faults control scale, structural style, and linkage evolution of fractures. Fractures formed over multiple periods. Many fractures in Cretaceous sandstones formed recently whereas some of those in carbonate rocks formed in the Paleozoic when strata were buried less than 5000 m. With the increase in burial depth, fracture porosity (and, probably) connectivity is reduced by mineral deposits. Fracture-forming processes include overpressure, present in situ burial and tectonic loading. Other variables modifying fractures include when fractures formed (timing), regional and local structural position, and scale and fluid flow leading to heterogeneity in whether fractures are mineral filled, open, or enhanced by dissolution. Our review provides insights into the origins, characteristics, evolution, and effectiveness of fractures in ultra-deep sandstone and carbonate rocks. • Ultra-deep reservoirs develop natural fractures of tectonic, diagenetic, tectonic-diagenetic, and overpressure origins. • Fault-related folds and strike-slip faults are the foundational factors for controlling ultra-deep fracture development. • Natural fractures in ultra-deep reservoirs are mainly formed when their strata depth is less than 5000m. • Structural diagenesis, overpressure, and present in-situ stress affect the fracture effectiveness in ultra-deep reservoirs. [ABSTRACT FROM AUTHOR]