BAIDUNZI-XIAOXUGONG DUCTILE SHEAR ZONE AND ITS ORE-CONTROLLING EFFECT IN THE SOUTHERN BEISHAN AREA, GANSU
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摘要: 白墩子—小西弓韧性剪切带是甘肃北山地区8条韧性剪切带中最南侧的一条, 位于北山南带的白墩子—小西弓一带, 呈近东西向展布, 长160km, 宽5~8km。该韧性剪切带以近水平右行剪切为特点, 是一条形成于中低—中偏高温度、较低差应力条件(53~106MPa)下的韧性剪切带, 主应变(Rxz)为4~20, 剪应变(γ)1.41~2.42, 剪位移达10~25km。该韧性剪切带对金矿床控制作用明显, 在区域上控制金矿床(点)的分布, 在矿床范围内控制金矿化带、矿体的形态、产状和规模。压扭性韧性剪切变形特点决定了金矿化类型以蚀变糜棱岩型为主, 蚀变以交代作用为特色。金矿化稍晚于韧性变形。Abstract: The Baidunzi-Xiaoxigong ductile shear zone, as the southernmost one of the eight ductile shear zones in the Beishan area, Gansu, is situated at the southern border of the southern Beishan area and near the northern border of the Dunhuang massif.It extents in a nearly E-W direction with a length of 160 km and a width of 5-8 km.This shear zone is characterized by subhorizontal dextral shear and formed under the conditions of low-middle to middle-slightly high temperatures and relatively low differential structural stresses (53-106 MPa).The principal strain (Rxz)is 4-20, the shear strain (γ)is 1.41-2.42 and the shear displacement is up to 10-25 km.The ductile shear zone has a marked controlling effect on gold deposits:it controls the distribution of gold deposits (occurrences)on a regional scale and the shape, attitude and size of gold mineralization zones and orebodies on a deposit scale.The features of transpressional ductile deformation determine that gold mineralization is mainly of altered mylonite type and that alteration is featured by metasomatism.Gold mineralization occurred a little later than ductile shear deformation.
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Key words:
- ductile shear zone /
- deformation /
- ore-controlling effect /
- Baidunzi-Xiaoxigong area /
- Gansu province
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图 2 白墩子-小西弓韧性剪切带面理线理产状投影图
下半球投影, A.面理极点投影; B.线理投影
Figure 2. Projections of foliations and lineations of the Baiduzi-Xiaoxigong ductile shear zone (hemispheric projections from bottom to top)
图 3 白墩子之东韧性剪切带中含金石英脉分布与糜棱岩面理的关系
1.花岗质糜棱岩; 2.含金石英脉; 3.产状; 4.地质点及编号
Figure 3. Relation between Au-bearing quartz veins and mylonite schistosity
表 1 白墩子-小西弓韧性剪切带糜棱岩岩石有限应变测量结果
Table 1. Finite strain measurements of mylonites in the Baidunzi-Xiaoxigong ductile shear zone
表 2 由定向薄片显微构造S-C面理夹角测算的剪应变
Table 2. Shear strains calculated from angles between S-C foliations of oriented thin sections of mylonite
表 3 显微构造反映的构造运动方向
Table 3. Sense of movement of the ductile shear zone
表 4 糜棱岩构造差应力估算结果
Table 4. Differential stress estimates of mylonites
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