The genesis and gold mineralization of the crypto‐explosive breccia pipe in the Yixingzhai gold region, central North China Craton

Abstract

The Yixingzhai gold deposit is a quartz‐vein–type deposit accompanied by skarn iron and porphyry molybdenum mineralization. There are four crypto‐explosive breccia pipes which provide an important ore‐controlling structure. Here we investigate the composition and compositional zoning of the native gold, garnet, and epidote in the Tietangdong skarn breccia pipe through detailed petrography, electron probe microanalysis, and elemental mapping. The native gold compositions show that they were formed in a relative higher temperature condition. Based on their composition and optical characteristics, the zoning in garnet can be divided into three types. The garnets of Generations 1 and 3 show high contents of spessartine (2.91–10.17 mol%) and grossular (20.94–54.71 mol%) and anomalous birefringence, indicating that they formed under relatively higher pressure and temperature and lower oxygen fugacity. The garnets of Generation 2 are mainly composed of andradite (75.70–99.98 mol%) and show compositional homogeneity, with formation under relative lower pressure and temperature and higher oxygen fugacity conditions. Magmatic‐hydrothermal pulses and multiple crypto‐explosions could be the main geological processes that caused the formation of the zoning textures. Zoning in epidote is more complex than that in garnet, and from core to the rim, the iron content shows an abrupt increase and aluminium content shows decrease. There is also decrease in iron and increase in aluminium in the inner part. These features might record multiple crypto‐explosion processes. Combining the complex replacement features of iron oxides and sulphides in the breccia pipe, we suggest that the Tietangdong breccia pipe formed through several crypto‐explosions. The fluid system in the breccia pipe activated during multiple crypto‐explosions, and oxygen fugacity varied greatly, which was disadvantageous to the accumulation and precipitation of ore‐forming elements. Crypto‐explosions destroyed the ore bodies formed during the early stage, resulting in their scattered distribution throughout the breccia pipe. Cone fractures formed eventually with the shrinking of the cooling breccia pipe after the magmatism ceased. Those fractures provided important ore‐hosting structures for the gold mineralization during the late stage. Our research indicates that there is high prospecting potential for porphyry Mo, Cu, and Au deposits in the deeper domains of the breccia pipes.

Pressure Controlled Permeability in a Conduit Filled with Fractured Hydrothermal Breccia Reconstructed from Ballistics from Whakaari (White Island), New Zealand

“…Past studies of magmatic conduits and breccias reveal insights into magma flow, outgassing, and fragmentation processes [4][5][6][7]. Detailed studies of hydrothermal breccia filled conduits, however, are dispersed between the maar diatreme, hydrothermal mineralization, and petroleum basin literature [2,[8][9][10][11] and are rarely applied to eruption models.…”

Tracing the genesis of skarn‐type iron deposit in central North China Craton: Insights from mineral zoning textures in ore‐forming intrusion

“…Compositional zoning in minerals records important information on magmatic, metamorphic, and hydrothermal processes (Zhang et al, ). Plagioclase is the most common rock‐forming mineral with zoning texture.…”

Halogen fractionation during vapor-brine phase separation revealed by in situ Cl, Br, and I analysis of scapolite from the Yixingzhai gold deposit, North China Craton

“…The Tietangdong Fe-Au skarn breccia pipe is located at the Yixingzhai gold deposit in the Taihangshan district, North China Craton (Zhang et al 2019). Scapolite commonly This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.…”