Origin Of Breccia And Its Metallogenesis Of Mayuan Lead-zinc Deposit

Mayuan lead-zinc deposit in Nanzheng county of Shaanxi province are located in Sinian Dengying formation strata, northern margin of Yangtze plate,which have a great prospecting potential. Over the last decades, a lot of studies have been done on the diagenetic mineral sources and metallogenic mechanism of Mayuan lead-zinc deposit by many researchers, and abundant progress has been made. Most geologists maintain that Mayuan lead-zinc deposit is similar to Mississippi Valley-type lead-zinc deposit. lead-zinc deposit in this area are controlled by three factors: basement structure, cover structure, breccia zone. The ore bodies are filled in tensile fracture and various broken belts, and the deposit occurs in Upper Sinian Dengying formation brecciated dolomite,controlled by layer,lithology, and secondary fault. Occurrence of the deposit is in accordance with that of Dengying formation strata. The more developed the tectonic breccias, the high extent of mineralization degree. The brecciated ores, as the special ore structure of Mayuan lead-zinc deposit, have noted by many researchers. The breccias are treated as indicator of ore prospecting, but the specific characteristics and genesis of breccias and brecciated ores in Mayuan lead-zinc deposit have not been studied intensively.The types of breccias were divided, and spatial distribution characteristics and petrological properties and their relationship with mineralization were studied, what’s more,the genesis and metallogenic significances of breccia were discussed based on geological survey on Mayuan region, petrography observation, electron probe analysis, combined with rock characteristics, mechanical characteristics of breccias, and tectonic uplift in Beiba area. The conclusions are as follows:The breccias in Mayuan lead-zinc deposit can be divided into three types: initial crack rock, tectonic breccias and cataclasite, which are based on the structure, construction, fragment extent, and difference in mechanical properties of rocks.Due to the impact of tectonic uplift, interlayer gliding and sliding occurs in Sinian Dengying formation strata, so that the thick-bedded dolomites in the upper section of Dengying formation fractured in tensile, and were crushed and broken. After displacement, the crushed dolomites were cemented to form breccias. Meanwhile, the Ore-hosting structure system of Ma Yuan lead-zinc deposit, namely Breccia shatter zone and radial horizontal fault, were formed.The ore- hosting layer of Mayuan lead-zinc deposit is the third lithostrome of upper part of Sinian Dengying formation. The mineralization degree is positive related with developed extent of tectonic breccias. Due to tectonic uplift, massive mineralization hot water circulation system was formed below the plate. By continuously extracting and absorbing Pb, Zn and other helpful components from basement complex, and organic-rich from algae dolomite in bottom of Dengying formation, the hot brine with abundant of organic and Pb, Zn,Ba and other ingredients was formed. Meanwhile, due to crustal rising and basement uplifting, resulting in interlayer sliding occurs in the upper Sinian Dengying strata and broken breccia belt was formed. Consequently, the ore-bearing brine was migrated to interlayer tectonic breccia belt to form deposit.