Typomorphic Features of Placer Gold from the Billyakh Tectonic Melange Zone of the Anabar Shield and Its Potential Ore Sources (Northeastern Siberian Platform)

Boris Gerasimov,Vasily Beryozkin,Alexander Kravchenko

doi:10.3390/min10030281

Abstract

Precambrian shields and outcropped Precambrian rock complexes in the Arctic may serve as the most important sources of various types of mineral raw materials, including gold. The gold potential of the Anabar shield in the territory of Siberia has, thus far, been poorly studied. A number of primary and placer gold occurrences have been discovered there, but criteria for the prediction of and search for gold mineralization remain unclear. The main purpose of this paper was to study the typomorphic features of placer gold in the central part of the Billyakh tectonic mélange zone in the Anabar shield and to compare them to mineralization from primary sources. To achieve this, we utilized common methods for mineralogical, petrographic, and mineragraphic analyses. Additionally, geochemical data were used. As a result of this investigation, important prospecting guides were identified, and essential criteria for the prediction of and search for gold deposits were elucidated. The characteristics of the studied placer gold were specific for gold derived from a proximal provenance. These characteristics included the poor roundness of the native gold grains, a cloddy–angular and dendritic form, an uneven surface, and a high content of coarse-fraction native gold (0.5–2 mm), which was as high as 24% of the volume of analyzed native gold. In addition, we conducted a study on the mineralogical features of the gold-sulfide mineralization that was disseminated throughout a small exposure area of paleo-Proterozoic para- and orthogneisses in the Anabar shield basement. A comparison of mineral inclusions in the coarse-fraction native gold and mineral assemblages in the ore deposits showed that one of the possible primary sources for placer gold might be small bodies of metasomatically altered orthogneisses associated with large granitoid plutons.

Highlights

The Anabar shield is a major element of the Arctic tectono-mineragenic belt
The study area covered the central part of the Billyakh tectonic mélange zone (TMZ) (Figure 1), which extends northwest for 250 km and is 30 km wide
It is important to emphasize that metal finds of this size are very rare for placers in eastern Siberia, which is typically dominated by very small (−0.25 mm) gold grains, representing more than 95% [36]

Summary

Introduction

The Anabar shield is a major element of the Arctic tectono-mineragenic belt. Despite the fact that most large and superlarge deposits of precious, radioactive, and rare-earth metals around the world are concentrated within shields, no economically important gold deposits have yet been discovered in the Anabar shield. The method of studying the evolution of minerals in placers can help to identify their potential ore bodies [1,2]. The study of the complex of placer gold typomorphic features is a highly effective way of predicting processes of gold mineralization on territories covered by Quaternary deposits, including the studied shield. The complex of placer gold typomorphic features (grain sizing, morphology, chemical composition, and mineral micro-inclusions) can be used as a means of exploration and evaluation throughout all stages of geological prospecting [3].

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Methods

Results

Discussion

Conclusion