La zona de deformación de Xiaoban experimentó alteración hidrotermal a temperaturas moderadas en el Mesozoico (180 Ma). Las muestras estudiadas corresponden a unidades alteradas e inalteradas provenientes de tres niveles en la mina. Después de un estudio sistemático de las fábricas de rocas magnéticas encontramos que: 1) La susceptibilidad se debe principalmente a la presencia de minerales paramagnéticos como la biotita y la pirita. La reducción de la susceptibilidad promedio se debe a la disminución de hierro y al cambio del tamaño del mineral magnético, así como al incremento de minerales diamagnéticos. 2) Decrecimiento de la anisotropía (P) después de la alteración hidrotermal. La tendencia al cambio es la misma que la de la susceptibilidad promedio. 3) El elipsoide de AMS no cambia sustancialmente su forma después de la alteración hidrotermal, y se mantiene una esfera oblada. El eje menor de susceptibilidad axial principal (K3) cae cerca del plano perpendicular al plano de equistosidad de todas las muestras. Sin embargo, el eje mayor de susceptibilidad axial principal está sujeto a grandes cambios. Los resultados indican que los nuevos minerales magnéticos están distribuidos en el plano existente de equistosidad, pero no tienen una orientación preferencial.
Low-angle faults include those occurring in thrust-nappe structures in a compressive setting and the detachment of metamorphic core complexes in an extensional setting. A11 low-angle faults have their own particularities. The low-angle fault plays an important role in controlling over some endogenetic metallic ore deposits. Based on studies of the Xiaoban gold deposit, Xinzhou gold deposit, and Longfengchang polymetallic ore deposit, and comparisons with other mines, the authors conclude the ore-controlling implications of low-angle faults as follows.(1) Because of high temperature and high pressure, as well as strong ductile deformation, the internal energy of the elements rises in the large-scale deep ductile low-angle faults, which causes the elements to activate and differentiate from the source rocks, forming orebearing hydrothermal solution, and bring mineralization to happen. (2) When rising from depths and flowing along the low-angle faults, the ore-bearing hydrothermal solution will alter and replace the tectonites in the fault zone. The rocks of the hanging side and the heading side differ in lithology, texture and structure, which results in changes or dissimilarities of the physical-chemical conditions. This destroys the balance of the hydrothermal solution system and causes the dissolved ore-forming elements to precipitate; as a result, a deposit is formed. Therefore, the meso-shallow ductile-brittle low-angle faults play the role of a geochemical interface in the process of mineralization. (3) Low-angle faults are often one of the important host structures.
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