Source of ore-forming material for the Huangtuliang gold deposit, Hebei Province and ore prospecting in the deep periphery

Abstract

The Huangtuliang gold deposit is characterized by its wide and large ore belt, stable extension and closely spaced orebodies. Unfortunately, no orebody was found by deep drilling. As a result, ore prospecting in this region was once put into dilemma. Detailed analysis of ore-forming and ore-controlling structures in the mining district by the authors has revealed that the ore-forming and ore-controlling structure in this mining district is a steeply dipping (85°−110°/∠70°–85° N-NNE), spade-shaped ductile shear zone, and the ore-controlling structures are a series of nearly erected second-ordered faults which are developed in the upper part of the ductile shear zone, intersecting with the ductile shear zone. Deep cutting of the ductile shear zone made it possible the ascending of ore fluids from the mantle plume at depth and these ore fluids would migrate upwards along the ductile shear zone under certain temperature and pressure conditions. Along their ascending path, the ore fluids would extract ore-forming elements from the country rocks and the extracted ore-forming elements would be deposited as ores in the hanging-wall second-ordered faults. The reason why no orebody was found in early prospecting at depth is that northward-dipping drilling in the southern part of the shear zone extended so deeply as to be beneath the shear zone. Only shallow-level orebodies could be found by southward-dipping drilling practice in the northern part of the shear zone. The location where deep-seated orebodies occurred shifted northwards and the orebodies occurred at greater depth. Therefore, it is natural that no orebody could be found when drill core passed through the shear zone. After the ore-forming and ore-controlling structures were well understood, the focus of ore prospecting was placed on the deep-level, northward-penetrating veins. In this way a number of new blind orebodies of great thickness have been found. On the basis of research development in the mining district, a prospecting plan has been made for ore prospecting in the periphery of eastern mining district. Prospecting practice has shown that there occur generally continuous engineering orebodies at large intervals. So, the Huangtuliang gold deposit has turned at one stroke from a medium sized to a large-sized, even a super-large gold deposit between prospecting lines 30–98.