Peculiarities of pyrrhotite mineralization in the Chertovo Koryto deposit (Patom Uplands)

Pyrrhotite mineralization of black shale gold-ore deposit in the central part of Chertovo Koryto (Patom Uplands) was studied. It was found that pyrrhotite consists of three generations, containing hexagonal and monoclinic modifications in various proportions. The increase in the monoclinic modification from the earlier to later generation was observed.

Changes in pyrrhotite composition are connected with variable physicochemical conditions of mineral genesis and cause different structural characteristics, mechanical and magnetic properties. In hydrothermal ore deposits pyrrhotite can be found in hexagonal and monoclinic modifications.
The present article describes the study results of pyrrhotite mineralization characteristics in the Chertovo Koryto gold-ore deposit, as well as the chemical composition of pyrrhotites.

Research methods
To carry out the research core samples were taken from 4 cross-bedding profiles, including two intersecting profiles and one from each opposite cross-bedding. Wells were drilled at full productivity of the ore body with access to the barren area. The drilled depth varies from 150 to 250 m. Core samples were selected thoroughly at intervals from 10 to 50 cm. Firstly, the core samples were studied macroscopically, and samples containing sulphide mineralization, including pyrrhotite, were selected. Then, the polished sections were made for the mineral-graphic study and implementation of pointcounter X-ray fluorescence analysis. The polarizing microscope Zeiss Imager A2m was used to carry out the optical study. The chemical composition was studied at the X-ray fluorescence microscope XGT-7200. 184 point-counter measurements were carried out.

Geological structure of deposit
This deposit is located in the north of Patom upland within the Big Patom river basin. The ore deposit was formed in the early Proterozoic carbonaceous terrigenous slates of Mikhailovskoe suite. The suite

Results and discussion
Pyrrhotite is represented by three generations. The generations are separated according to the polishing characteristics, morphology of aggregates, and paragenetic mineral associations.
Pyrrhotite I forms "striates" parallel to the foliation of carbonaceous shales ( fig. 1a). It has a eugranitic internal structure. "Striates" size varies in the range of 0.

Discussion and conclusion
During the research, it was found that in the Chertovo Koryto deposit pyrrhotite is represented by three generations, distinguished by the polishing, morphology of aggregates, paragenetic mineral associations and a range of impurity elements. Generations of pyrrhotines are distributed equally in the ore body. Pyrrhotite I occurs throughout the ore deposit both in the ore and non-ore intervals. Pyrrhotite II and III occur in the central part of the ore body, where rich concentrations of gold intervals are located. All three pyrrhotites are characterized by similar iron content, but different nickel content. The highest nickel content was found in pyrrhotites of I and II generations in the amount of 0.284 and 0.318 wt.%. The presence of nickel indicates textural deformations in sulfide structure. Hexagonal and monoclinic modifications are found in pyrrhotites of all generations ( fig. 2). However, the amount of monoclinic modification increases from early to late generation.