Geology and mineralogy of ore at the hidden Engteri Au-Ag deposit,the Magadan Region |
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| Authors: | A V Obushkov S F Struzhkov M V Natalenko O B Ryzhov S G Kryazhev Yu I Radchenko |
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| Institution: | 1.Central Research Institute of Geological Exploration for Base and Precious Metals,Ministry of Natural Resources and Ecology of the Russian Federation,Moscow,Russia;2.Dukat Mining and Geological Company,Magadan,Russia |
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| Abstract: | The Engteri is a new hidden Au-Ag deposit in the Russian segment of the Pacific ore belt. The discovery of this deposit merits
special attention, because it involves repeated attempts to reappraise a lowprospective ore occurrence, which were crowned
with success as a result of fulfillment of large-scale drilling project. The average Au grade is 18.6 gpt. The deposit is
classified as the gold geochemical type of Au-Ag deposits. The major ore mineral is pyrite, which amounts to no less than
95% of the total ore minerals. The native phases comprise electrum and to a lesser extent native gold of low fineness (730).
The homogenization temperature of fluid inclusions is 125–255°C with a distinct maximum at 145–150°C. Despite blind localization
of some orebodies, the Engteri deposits bears evidence for a deep erosion level: (1) small vertical range of economic mineralization
(50–100 m); (2) predominant occurrence of massive sugarlike quartz with a low sulfide content; (3) prevalence of massive and
brecciated textures above rhythmically banded textures; and (4) lack of low-temperature propylites. The southern part of the
ore field distinguished by occurrence of rhythmically banded, framework-tabular, and brecciated texture has the best prospect
for revealing new orebodies. The Engteri deposit allowed us to outline the following prospecting guides and methods of prospecting
for hidden Au-Ag deposits: (1) these deposits are regularly arranged in ore clusters between heavy concentrate anomalies of
cinnabar and gold-silver or silver-base-metal occurrences (method of missed link); (2) findings of fragments of ore mineral
assemblages with sporadically high Au and Ag contents in barren calcite-quartz veins (method of indicators); (3) linear zones
of ankeritization in the fields of low- and mediumtemperature propylites (mapping of metasomatic rocks); and (4) pyrite-quartz
veinlets with rhythmically banded pockets (mineralogical mapping of halos of stringer-disseminated mineralization). |
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