Research For Geophysical Characteristics And Prospecting Application On Huangshan-Jingerquan Ultramafic Complex Belt In Eastern Tianshan Of Xinjiang

Huangshan-Jingerquan ultramafic complex zone is located in the eastern part of thefamous Kanggur large-scale fault belt, eastern Tianshan, which is over200kilometers longand a ductile shear zone of multi-phases and-levels. There are many mafic and ultramaficcomplexes with over30magma Cu-Ni sulfide deposits along the fault belt. The fault may cutat much depth and the mantle-derived magma intruded evidently. It is helpful to carry out theresearch on the geophysical field’s characteristics for improving the interpretation level of thegeophysical anomaly and the prospecting detectability, and resolving the deep structuralproblems understanding and delineating the intrusions range and evaluating the ore-bearingability of the rock mass, also which will make a significant propelling for the furtherprospecting studies on the regional resources.On the gravitational and magnetic anomaly map with the scale of1to200,000,Huangshan--Jingerquan ductile shear zone corresponds to the anomalies of gravity andmagnetic gradient belt exactly with the same trends and approximate length. The values of thegradient zonal anomalies is higher from south to north with the characteristics of "step"anomalies, and which indicated that there is a density and magnetic interface with the lowervalue southwards and the higher value northwards between the both sides of the shear zone.The model calculation prove that the position of maximum Vxz of directional derivative ofthe "step" Bouguer Anomaly (Δg) is in accordance with the projection location of the densityinterface on the ground, and which is unrelated to the tendency of the "step” and relatedslightly to the dip of the "step”. It is defined that the projection position of the densityinterface on the surface accords to the location of Huangshan-Jingerquan Fracture (F11)basically, according to location of the maximum Vxz that is calculated Δg. According to theforward modeling for the “step” from Δg and Vxz, the buried depth (h) of the top of the step isfrom2km to3km underneath, and the extending depth (H) of the bottom is more than10kmwith the density contrast (σ) of0.1to0.2×10~3kg/m3. All the above indicate that this densityinterface extends very deeper downward with obvious difference of density. It is concludedthat the magnetic bodies of AM-2and AM-3is tilt to north steeply with the buried top depthof5km to6km and extend downward greatly, through the processing of “reduce to magnetic pole”and “conversion between field components” and “upward continuation” for theaeromagnetic ΔT. The regional gravity and magnetic anomalies show that the huge densitycontrast interface and a magnetic body exist beneath this ductile shear belt, therefore it ispossible that there is a deep faults and channels for mantle-derived magma in this ductileshearing belt.Based on the characteristics of the shape and scale and occurrence of ore-bearing rockmass in three typical copper-nickel sulfide deposits and their lithofacies and mineralassemblage, as well as the physical parameters of rock and ore, it is compared and analyzedfor the intensity and scale of anomalies of gravity and magnetic and resistivity andpolarizability within the three mines area in this thesis, revealing the internal causes andexternal conditions of the generation of geophysical composite anomalies of "three higher andone lower" formed in the capable ore-bearing rock mass with higher magnetic force andhigher gravity and higher polarizability and lower resistivity. The optimal methods ofgeophysical prospecting for searching of this type rock mass is summed up, of whichcomprises the surveying of "gravity and magnetic and electric method". As for thecharacteristic of these magmatic sulfide deposits that “mineralization occurred in the smallerintrusive”, the geophysical prospecting model is is put forward with that “closer and smallerand higher”，which is "Approach the field source as close as possible, shorten the pointspacing as smaller as possible, increase the accuracy of the field measurement and thepositioning as higher as possible", of which means to maximize the effect of geophysicalprospecting method on this belt.