犁式正断层特征及其在找矿预测中的作用:以黔东松桃西溪堡大型锰矿床为例

犁式正断层是在局部或区域张应力体制下形成,产生于伸展体制下有韧性岩石垫底的脆性岩石中。犁式正断层在平面上呈弯曲状,断层两侧发育次级断层,具分支复合特征;在剖面上,随深度增加,断层倾角逐渐变缓,并且形成分支产状较陡的次级断层,断距逐渐变大。黔东松桃西溪堡大型锰矿床发育的F₁断层为犁式正断层,其发生伸展作用的时间应与早白垩世区域挤压构造体制向伸展构造体制转换的时间一致。整个F₁断层及其分支断层造成含锰岩系呈阶梯状下降拉伸,造成含锰岩系的不连续,越往深部,断层滑脱面越趋于平缓,拉空带宽度愈加增加。该断层及其次级断层将含锰岩系破坏并断切为几个部分,影响了含锰岩系的连续性,形成矿体-拉空带-矿体这种空间组合形态。F₁断层上盘的下降,造成了上盘含锰岩系的埋深加大。因此,在找矿预测中,应充分考虑断层断距差异,合理圈出拉空带,从而避免在探矿过程中打到拉空带。 

Characteristics of Listric Normal Fault and Its Role in Prospecting Prediction:An Example from Xixibao Large Manganese Deposit,Songtao County,East of Guizhou Province

Listric normal fault is formed under the system of local or regional tensile stress,produced in the stretch of resilient rock bottom under the system of brittle rocks.Listric normal fault in the plane is bent and secondary faults on both sides of the fault are featured by branch compound.In profile,with depth increase,the fault dip angle becomes gentle gradually and fault distance grows progressively,forming secondary faults with steep branch occurrence.F₁ fault developed in Xixibao large manganese deposit,Songtao in eastern Guizhou is a listric normal fault,whose stretching time should be consistent with the time of the transfer of early Cretaceous regional compression tectonic system to extension tectonic system.The entire F₁ fault and its branch fault causes the manganese-bearing rock series to fall and stetch in ladder shape,leading to the disconinuity of the mangnese-bearing series.The deeper the fault,the gentler the fault detachment plane and the wider the pulling zone.The fault and its secondary fault break the manganese-bearing rock series and cut it into several parts,affecting the continuity of the manganese-bearing rock series and forming a spatial association of ore body-empty band pulling-ore body.The falling of the upper wall of F₁ fault deepens the burial of the mangnese-bearing upper wall.Hence,we should take full account of the fault distance and scale rationally the empty belt in mineral prediction so as to prevent the exploration from drilling into the empty belt.