Research On Ore-controlling Characteristics In Yangshan Gold Belt, Wen County, Gansu Province

Yangshan ore belts,located in the triangle region named as“gold delta”of Shaanxi,Gansu and Sichuan provinces, is the largest micro- disseminated gold deposit in China. It is situated in the Wenxian tectonic arc which belongs to the tectonic junction of Yangtze block,Sino-Korean plate and Songpan-Ganze block .Yangshan gold deposit is classified as magmatic hydrothermal type and formed approximately in early Jurassic. Since Late Triassic, Paleo-Tethyan was gradually closed down along Qinling mountain belt. As a result, a fold–thrust belt composed of Anchanghe—Guanyinba fault and Getiaowan—Caoping anticlinorium was formed because of the N-S direction compression in Yangshan area, which control the ore body characteristics.Late Triassic to early Jurassic is the main ore-forming period of Yangshan gold belts and during this time, there is a series of large scale intermediate-acid magmatic intrusion regionally. At the same time ,a number of granite porphyry dikes emerged in Yangshan area, and consequently the ore deposits were formed as a result of gold-contained hydrothermal alternation.Anchanghe—guanyinba fault belt composed of three secondary fault groups, is the main fault in Yangshan area and its strike control the distribution of gold ore bodies, its mechanical property determine the mineralization type of gold. Yangshan gold belt is generally comprise of four sub deposits such as Yangshan, Gaoloushan, Anba, Getiaowan ,the distribution of which correspond to the extension of Anchanghe—guanyinba fault belt.Compression-shear fault belts in NEE and NWW direction usually contain massive, thin-veined and micro- disseminated type ore bodies. Tension faults in approximately N-S direction are prone to be filled with gold-contained hydrothermal fluids and form thick-veined ore bodies.Third and fourth members of the Sanhekou group of Middle Devonian are composed of green facies schists, which experienced multiple-stage metamorphism and formed a series of foliations. They are usually the host rock of gold because of their anisotropy. Its distinct property is the foliation transposition. In macroscopical scale, each rock member exhibit different deformation behavior because of their contrast in strength. Phyllites occur like plastic flows and act as matrix, in the contrary, quartz sandstones and limestones form both non-rooted flods like hook in geometry and boudins the major axis of which correspond to the strike of the schist foliation.Generally speaking, the main structures of Yangshan ore belts were formed as a result of N-S direction compression in indosinian period. The fold–thrust belt composed of Anchanghe—Guanyinba fault and Getiaowan—Caoping anticlinorium control the gold mineralization characteristics.