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Publié par | fewyang0 |
Nombre de lectures | 35 |
Langue | English |
Poids de l'ouvrage | 4 Mo |
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Observations of the Nasedkino gold skarn deposits,
eastern Siberia, Russian Federation
Peter J. Pollard
Pollard Geological Services Pty. Ltd.
7 Jillinda Place, The Gap, Queensland, Australia 4061
peter@peterpollard.com
November, 2010
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Pollard Geological Services Pty. Ltd. Nasedkino gold skarns, Siberia 3
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Executive Summary
The Nasedkino skarns have all of the major characteristics of the oxidized class of
gold skarn deposits. These include the presence of andraditic garnet, diopsidic
pyroxene, tremolite-actinolite, pyrite, and hematite, together with a high garnet :
pyroxene ratio, low total sulfide content, pyrite>>pyrrhotite and ubiquitous
occurrence of chalcopyrite. Skarn formation and gold mineralization post-date the
metamorphism and ductile deformation which are present in the host quartzo-
feldspathic gneisses.
The general paragenesis of skarn formation comprises:
K-feldspar alteration ± pyroxene
Brown garnet-green pyroxene-amphibole-quartz skarn
Epidote-actinolite-carbonate alteration
Pale creamy garnet breccia
Quartz-K-feldspar-pyrite-chalcopyrite-molybdenite-hematite-actinolite-chlorite-
epidote-carbonate veining and alteration
Pyrite ± sericite veins and alteration
The host rocks also contain alteration and mineralization represented mainly by:
Biotite veins and alteration olybdenite-hematite-actinolite-chlorite-
epidote-carbonate veining and alteration
Pyrite-sericite veins and alteration
In addition, late hydrothermal stages including tourmaline-pyrite veins and low-
sulphidation epithermal veins overprint the skarns and their host rocks. These appear
to be unrelated to the hydrothermal system that produced the gold skarns.
Biotite alteration and quartz-K-feldspar veins form a broad halo to the skarn deposits
and should prove useful as an indicator of proximity to skarn in exploration drilling.
• It is recommended that further exploration for gold skarns in the Nasedkino
district focus initially on IP chargeability highs similar to those that
characterize the known deposits, especially where they coincide with
northwest-trending fracture systems.
• It is recommended that detailed sampling of the low-sulphidation epithermal
veins be carried out in order to assess their prospectivity for precious metals
mineralization.
• It is recommended that an exploration program be developed aimed at
discovery of porphyry copper(-molybdenum-gold) systems which are highly
likely to be present within the same magmatic arc as the Jurassic gold skarns.
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Pollard Geological Services Pty. Ltd. Nasedkino gold skarns, Siberia
4
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Table of Contents
……………………………............................................................................................2
Executive Summary.......................................................................................................3
Table of Contents...........................................................................................................4
Introduction and scope of work .....................................................................................5
Geological setting and host rocks ..................................................................................7
Plagioclase-quartz-biotite gneiss ...............................................................................7
Plagioclase-quartz-hornblende gneiss........................................................................8
Plagioclase-quartz-garnet-biotite gneiss ....................................................................9
Granite and pegmatite ..............................................................................................10
Amphibolite .............................................................................................................11
Post-deformation intrusions.....................................................................................12
Comments on metamorphic grade ...........................................................................14
Alteration and mineralization ......................................................................................15
Skarn alteration and mineralization .........................................................................16
K-feldspar ............................................................................................................16
Pyroxene ..............................................................................................................17
Garnet-pyroxene-amphibole-biotite-quartz skarn................................................19
Garnet Breccia .....................................................................................................21
Retrograde alteration and mineralization.................................................................24
Host rock alteration and mi...................................................................28
Sericite ± epidote ± quartz ...................................................................................28
Biotite veins and alteration ..................................................................................29
K-feldspar-quartz ± actinolite ± magnetite ± hematite ± pyrite ± chalcopyrite ±
molybdenite ± arsenopyrite ± chlorite ± epidote ± calcite veins .........................30
Sericite .................................................................................................................33
Other vein and alteration styles................................................................................34
Pyrite veins...........................................................................................................34
Tourmaline-pyrite veins.......................................................................................35
Low-sulphidation epithermal veins......................................................................36
Paragenesis of alteration and mineralization ...............................................................38
Timing and sites of gold and copper mineralization....................................................39
Comparison with other gold skarns .............................................................................41
Exploration...................................................................................................................43
Nasedkino ................................................................................................................43
Porphyry Cu(-Au-Mo) deposits ...............................................................................43
Epithermal precious metal deposits .........................................................................44
Discussion and recommendations................................................................................45
References....................................................................................................................47
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Pollard Geological Services Pty. Ltd. Nasedkino gold skarns, Siberia
5
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Introduction and scope of work
The Nasedkino gold skarn deposits are located in eastern Siberia approximately 16km
from the Trans-Siberian railway station at Arteushka. At the request of Mr. Gary
st thArtmont of Intergeo the author visited the area from 21 -29 September 2010 to
review drill core from the deposits and visit outcrops in the surrounding district.
The scope of work as defined in the contract for this study includes the following:
• Review the geology of the Nasedkino deposits and Uryum property and
inspect drill core from certain key sections through the Pridolinny, Zhelanny,
Gora 5 and North West deposits.
• Determine if the skarns from each deposit are related to the same causative
source, the composition of the original host rock and if there is a definable
marker horizon present in the mineralized section.
• Determine the mineralogy of the mineralized and non mineralized skarn,
paragenesis of the alteration sequences, and compare Nasedkino with other
skarn deposits.
• Summarize observations in a technical report which addresses the setting of
the Nasedkino deposits, characteristics of the alteration and mineralization and
recom