Research On Metallization Of The Qixiashan Lead-zinc-silver Polymetallic Deposit, Jiangsu Province, China

Qixiashan Lead-zinc-silver polymetallic deposit is the largest Lead-zinc deposit in East China. This deposit is also an important part of the Ningzhen ore concentration area. This deposit is a typical deposit controlled by the Silico-calcium lithologic interface at the extro-contact. Previous comprehending about the genesis of no invasion of the exposure limits this deposit. I studied the metallogenesis of this deposit using geochemistry of mineral deposits and fluid inclusion tools.The Qixiashan deposit is present at the Silico-calcium lithologic interfaceamong the Jurassic sandstone and the Huanglong Formation carbonate rock, the Wutong Formation quartz-sandstone, and the Carboniferous-Permian limestone. The ore bodies are primarily present at the calcium-rich part of the Silico-calcium lithologic interface. The structures controlling the formation of the deposit are the NEE-trending faults, the unconformity, the NWW-trending faults, and the fossil karst. Silicification is the alteration closely related to the mineralization.According to the study of petrography, mineralogy, rock geochemistry and chronology in the Qixiashan deposit formed at the late period of the Early Cretaceous Epoch. It is referred that an acidic intrusion hid below the Da’ao Mountain controlled the formation of this deposit and the emplacement of the intrusion was related to the Tangshan-Zhenjiang magmatic activities in the Ningzhen Region.The analysis of geochemical sections, stable isotopes and rare earth elements show that the metallogenetic materials principally stemmed from the magma, part of them were extracted from the wall rocks that are circulated by the fluids flowing through; the magmatic-hydrothermal fluids are the primary ore-forming fluids type. With the ore-forming processes going, some amount of meteoric fluids was involved,which has the tendency to increase. The study of fluid inclusions manifest that the ore-forming fluid is low salinity, high to intermediated temperature and intermediate density fluids. The fluid system is a Cl-enriched H2O-Na Cl. The temperature, salinity and pressure of ore-forming fluids tend to decrease with the evolution of the ore-forming processes.We first study the ore-forming mechanism of Qixiashan deposit basing on the influences of a Silico-calcium lithologic interface on the metallogenic processes. We disclose the constraints of the change of the physicochemical conditions of Silico-calcium lithologic interface on the minerals’ crystallization. Through studying the migration and precipitation of different elements, we confirm that Silico-calcium lithologic interface constrains this deposit belongs to low to intermediate temperature deposit type. In addition, we construct “trinity model” of geological prospecting prediction for mineral prospecting in Qixiashan deposit.