Session 5 Epigenetic gold systems - Extra Materials - Springer

Chapter 5-5
Geology and ore genesis of the Nanjinshan gold
deposit in Beishan Mountain area, northwestern
China
Si-hong Jiang, Feng-jun Nie
Institute of Mineral Resources, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, Beijing, 100037, China
Abstract. Located in the western part of the Beishan Mountain area,
the Nanjinshan gold deposit occurs within Carboniferous pyroclastic
rocks. The ore geology of this deposit is described and its origin is
discussed in this paper. It can be concluded that the Nanjinshan
gold deposit was formed during Indosinian (250~205Ma)
magmatism, and belongs to the intrusion-related, meso- to epi- thermal
type of gold deposit.
Keywords. Deposit geology, ore genesis, gold deposit, Nanjinshan,
Beishan Mountain area, China
1 Introduction
Located in the western part of Tianshan-Yinshan-Great
Hinggan metallogenic belt, and the conjunction area of
Inner Mongolia Autonomous Region, Gansu Province and
Xinjiang Uygur Autonomous Region, Northwest China,
the Beishan Mountain area is one of the most important
gold metallogenic provinces in northwestern China. To date,
about 100 gold deposits and prospects have been discovered,
explored and mined, among which Nanjinshan,
Mazhuangshan, Liushashan, Jinwozi, Zhaobishan and
Xiaoxigong are the most important ones.
The Nanjinshan gold deposit is situated in the northwestern
part of Beishan Mountain (Mt.) area , and is the
first discovered through geochemical exploration in Gansu
province. It is important to study the ore deposit geology
and its genesis, in order to guide the mineral exploration
for gold in this area.
2 Geological setting
The Beishan Mt. area can be divided into three tectonic
units by the Liuyuan-Daqishan and Hongshishan-
Heiyingshan deep-seated faults (Zuo and He, 1990; Liu and
Wang, 1995; Nie et al., 2002) (Fig.1). These tectonic units
are (1) Tarim plate to the south, which is composed of
Dunhuang and Anbei-Jiusidun terranes from south to north,
respectively; (2) Kazakhstan plate, consisting of Liuyuan-
Daqishan, Huaniushan, Mazongshan, Gongpoquan-
Yueyashan and Hongshishan- Heiyingshan terranes from
south to north; and (3) Siberian plate, comprising
Queershan and Wuzhuergashun terranes. It is noted that
the area has been influenced by repeated distinct tectonomagmatic
activities.
2.1 Stratigraphic sequences
The oldest stratigraphic unit exposed in the Beishan Mt.
area is the Archean Dunhuang Group, which occurs in
the southernmost part of the area. It consists of quartzite,
gneiss, amphibolite, marble and schist, and constitutes
the basement of the Tarim plate.
The Proterozoic strata crop out in the Anbei-Jiusidun,
Huaniushan, Mazongshan and Hongshishan-Heiyingshan
terranes. They are mainly composed of granulite, schist,
marble, crystalline limestone and dolomite.
The early Paleozoic marine sedimentary and volcanic
rocks are located mainly in Mazongshan, Gongpoquan-
Yueyashan and Queershan terranes, which are composed
of rhyolite, dacite, andesite, basalt, tuff, sandstone, limestone,
slate and siltstone. In contrast, the late Paleozoic
marine sedimentary and volcanic rocks are widely distributed
in the Beishan Mt. area, and notably consist of
rhyolitic dacite, rhyolite, conglomerate, sandstone, limestone,
tuff and slate. They are one of the most important
host rocks for gold deposits in the area.
The Mesozoic and Cenozoic continental sedimentary
rocks are distributed primarily in basins developed
unconformably on the Precambrian and Paleozoic rocks.
The rocks comprise mainly sandstone, conglomerate and
shale.
2.2 Intrusions
Ultramafic to granitoid batholiths, stocks and dykes are
common throughout the Beishan Mt. area. The most common
intrusive bodies are Hercynian (405~250Ma), which
are distributed widely in the area as batholiths, stocks
and dyke swarms. These are composed of ultramafic rocks,
gabbro, quartz diorite, diorite, tonalite, granodiorite,
monzonitic granite and K-feldspar granite, which are
closely related to the formation of most gold deposits in
the area.
Indosinian (250~205Ma) and Yanshanian (205~66Ma)
granite and K-feldspar granite batholith and stocks mainly
crop out in the eastern and southeastern parts of the study
area. Some of the Indosinian intrusions have genetic relationships
with the formation of gold deposits in the region.
The Nanjinshan gold deposit is a typical example.
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