Structure of the Erdenet ore district according to gravimetric data

Abstract

The purpose of the study is construction of a model of the upper crust structure of the ore region in Mongolia and the three-dimensional mapping of intrusive bodies with which copper-porphyry mineralization is associated. An areal gravity survey was carried out with an observation density of 1 point per 6 km2 with the measurement accuracy of ±0.8 mGal. As a result, it was found that copper-molybdenum ore occurrences of the area including the Erdenet ore district are confined to local gravitational minima, which are interpreted as thickening of the body of the Selenga granitoids. The latter are confined to local depressions of this body base. The spatial proximity of supply channels of small ore-bearing intrusions and large granitoid bodies of the Selenga complex has been established. Porphyry ore intrusions are confined to rather wide (about 10 km) zones located above the depressions of the base of all intrusions of the Selenga complex (both granitoid and diorite). Since the local base depressions of the granitoid intrusions correspond to the position of magma supply channels, ore-bearing small intrusions were introduced approximately in the same places where the supply channels of granitoid intrusions of the Selenga complex existed. Therefore, it can be assumed that this case is characterized by not only tectonic inheritance (confined to the same faults and their intersection points), but also by a genetic one, since residual melts of the same foci, in which intrusion magma of the Selenga complex was generated might be the sources of small intrusions. From this point of view, the expediency of distinguishing an independent Erdenet complex seems to be controversial. Geophysical data on the spatial proximity of specified intrusion supply channels permit only to raise the question of such expediency. The solution to this issue is possible on the basis of a comprehensive analysis of petrological and geochemical data.