VOLUME 18 (3)/June 1988

I. Zagorčev, S. Moorbath. Rubidium-strontium isotopic data on the Paleozoic magmatism in the Trân District. Five whole-rock samples from biotite porphyroid granodiorites at the former mine “Zlata” define an isochron corresponding to an age of 414 ± 61 Ma, initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7058 ± 0.0013 and MSWD of 1.7. Therefore, the probable age of the latest intrusive phases of Ljuckan magmatic complex is Silurian. In view also of the predominantly gabbroic composition of the early magmatic phases it can be assumed that the whole complex was formed by consecutive intrusion and cooling of magmas produced through differentiation, fractionation and contamination of a primary magma of mantle origin. This igneous activity was of Caledonian age.

S. Bakurdziev, L. Ratiev, О. Zakhariev, D. Vundev, P. Mateev. Prognostication and estimation of ore-bearing by means of nonparametric regression analysis, estimation of vector potential and its gradient. Two methods- kriging and trend-analysis are broadly used in ore-bearing estimation and prognostication. Both have their advantages and disadvantages. A methodology combining advantages of above methods and minimizing their shortcomings is proposed and discussed here. For the purpose a program NPLRG is written (by Vundev and Mateev) providing: 1) prognostication within three-dimensional regular (or irregular) grid; 2) field selection; 3) scaling along X, Y, Z; 4) selection of weight function; 5) selection of the number of variables (M ≤ 1O) and of their combinations. At any given point are found: 1) number of observations evaluated in calculations; 2) prognostication of the mean content; 3) 5-% level of significance of the prognostication; 4) prognostication gradient along three axes and its variance. This method was tested on ore bodies of different type – stratiform, lenses, veins, porphyry deposits, ore-bearing faults, ore columns, deep marine deposits of manganese concretions. The program provides also simulation of ore bodies of any form and display of numeric and graphic data using microprocessor technics.

H. Dragiev. Role of Madan overthrust in generation of the metasomatic deposits Mogila and Osikovo in Central Rhodopes. The metasomatic Pb-Zn deposits in Central Rhodopes are related to several stratigraphic levels corresponding to carbonate formations. The most typical ones are located within the Madan ore field. Based on computer data processing of Mogila and Osikovo deposits are factors selected as controlling ore-bearing. Scarns are most informative prospecting and explorating criteria for ore bodies of this type. Pb-Zn mineralization, predominantly poor, is associated with post-mineral metasomatic quartz also. Computerized geometric evaluations show clear East-West orientation of ore bodies. This changes existing ideas of the indirect connection of W-NW faults and mineralization. Special attention is paid to the position and regional behaviour of the Madan overthrust. Its clarified new position introduces significant changes into lithostratigraphy of the ore field. The overthrust controls the thickness of rocks which, from lithostratigraphic view point, favor the generation of metasomatic deposits, prerequisites the range of mineralization and the anisotropy of the rock massif. The environmental model of metasomatic ore bodies generation is built up on the ground of the analysis made in this paper.

No abstract is available for this publication.