Morphology of the Gorikhinsky granite massif: a study by mathematical statistics methods

The Gorikhinsky granite massif is located in the marginal part of the Khentei highlands (Mongolian-Transbaikalian folded system, Central Mongolia). The massif is composed of coarse-grained weak-porphyry leucocratic granites, granite porphyry, and pegmatites. In the rocks of the massif, rock crystal deposits have been discovered. In certain pegmatite bodies, in addition to smoky quartz and morion crystals, the study has found the presence of fluorite, topaz, biotite, tourmaline, beryl, garnet, and allanite. The accessory minerals are cyrtolite, xenotime, zircon, sphene, rutile, apatite, cassiterite, etc. Thus, the study of the geological structure of the above object is of interest not only from a scientific but also from a practical point of view. The research data have become the basis for setting areal gravimetric work to determine the features of the massif’s geological structure. The work has been performed by the standard procedure using Scintrex Autograv CG-5 gravimeters. The height of the observation points has been determined by Trimble 5700 GPS devices. The RMS accuracy of the gravitational anomalies calculation as well as the density of the observation network meet the technical requirements for 1:100000 scale gravimetric surveys. Using the results of the gravity survey, a map of gravity anomalies in Bouguer has been compiled. Based on the interpretation of the map, with the use of the methods of mathematical statistics, quantitative characteristics of the shape and size of the body have been defined and a three-dimensional model of the massif has been built. For the purpose of the transformation and inversion of the gravitational field, the variance and regression methods of mathematical analysis have been used. The maximum thickness of the granites is 3.5 km; the area of the earth's surface projection is twice that of the granite outcrop. The obtained estimates are confirmed by the results of solving the inverse problem of gravimetry using the method of model selection. The article concludes that the use of the regression and variance analysis methods of mathematical statistics in the studies of the morphology of the intrusive bodies has proved most effective. The information on the shape and size of the massif will be used in concluding on the prospects of the massif’s metallogenic trend.

anomaly, inversion, granitoids, statistical analysis, petrophysical model

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