Integrated Geophysical and Geochemical Indicators of the Gejiu Tin Mine and Its Neighbouring Areas

Abstract

This paper deals briefly with the integrated geophysical and geochemical indicators of the metallogenic belt, ore districts, ore fields, deposits, and orebodies of Gejiu and neighbouring mineralized areas.

The metallogenic belt lies at the second order derivative negative anomaly of the regional Bouguer gravity field or at the gradient zone of alternating positive and negative anomalies, and is accompanied by geochemical anomalies.

The mining districts are all controlled by granites, folded fractures and certain lithologies. Because the granites are characterized by a lower density than the wall rocks, and by weak magnetism, the outcropping or concealed granite masses show low gravity and low magnetic anomalies, associated with geochemical anomalies.

The Gejiu tin ores are commonly distributed around the protuberances of granite masses concealed 200 m to over 1,000 m beneath the surface. Because the granites are over ten times lower than wall rocks in resistance, they can be delineated by the integrated indicators of anomalies for low-resistance bodies defined by electrical sounding corresponding with primary geochemical anomalies.

The integrated geophysical and geochemical indicators for tin fields neighbouring Gejiu consist of magnetic anomalies of certain size, A.C. dual frequency induced polarization anomalies, secondary and primary geochemical anomalies and the existence of ore-bearing layers at corresponding locations.

The orebodies are delimited by primary anomalies and composite profiling anomalies; orebodies between workings are delineated by the radiowave method.

Integrated geophysical and geochemical indicators over cassiterite-sulphide-type orebodies near Gejiu are quite similar to those over the ore fields. Elements such as Sn and Ware present over the Sn-Wquartz vein type orebodies with groups of quartz veins at corresponding sites.