Abstract:

Tsav, Jiawula, Chaganbulagen Ag-Pb-Zn deposits as well as Errentaolegai Ag deposit are located at northeastern part of the Northern China-Mongolia block (NCMB), and constitute the most important Ag-polymetalic ore cluster along the China-Mongolia border. The Ag-polymetallic ore deposits occur mainly in the Jurassic volcano-sedimentary rocks as thin veins, veinlets, sulfide-enriched pockets, breccias and lenses. The mineralization can be classified into two types: quartz-sulfide veins and carbonate-sulfide veins. Both of the two type veins have characteristics typical of intermediate sulfidation deposits worldwide. One of the most prominent features for the Ag-polymetallic deposits mentioned above is that they are spatially and temporally associated with Mesozoic Yanshanian alkaline or high-K calc-alkaline intrusive dykes (or sills). It should be pointed out that Jurassic volcanic strata consist of mainly shoshonite, trachyandesite, latite, and high-K, andesite, dacite and rhyolite as well as ignimbrite and tuffaceous rocks, while Yanshanian intrusions include monzonite, monzodiorite, diorite,granodiorite, granite and syenite. All these ore-bearing intrusive rocks are enriched in K,Ba, Th, Rb, Sr, Nb, La, Ag, Zn and Nd, and depleted in Ca, Mg, Co, Ni and Cr. All these geological evidences indicate that the collision of the amalgamated NCMB and  Siberian plate is likely to occur during the time span of Late Middle to Early Late Jurassic. Subsequent, post-collision lithospheric and crustal extension may lead to a large-scale magmatic activity and a great volume of fluid ascent. As a result, a number of Ag-polymetallic deposits and prospects were fromed in Tsav-Jiawula region. Tsav, Jiawula, Chaganbulagen and Errentaolegai deposits have differences on their geographic location, ore body geometry and mineral assemblage, but they have a lot of similarities on geodynamic setting, genetic type, and ore-forming process. Our studies show that most of Ag-polymetallic deposits and prospects are concentrated in jointed part of the Pre-Mesozoic upwelling consisting of Precambrian-Paleozoic strata and Jurassic volcano-sedimentary depression in the studied area. The NW and NS trending tensional fault zones, filled with high-K intrusive dykes would be the potential exploration targets for Ag-polymetallic deposits in  Tsav-Jiawula region at the easternmost part of China-Mongolia border.

Key words: silver-polymetallic deposit, Late Mesozoic, High K-calc-alkaline intrusive dyke, ore-forming processes, Tsav-Jiawula region, China-Mongolia border