http://www.sciencedirect.com/science/article/pii/S1674987111000764 |
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| Authors: | Guoxiang Chi Chunji Xue Hairuo Qing Wei Xue Jiangwei Zhang Yunqiang Sun |
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| Institution: | 1. Department of Geology, University of Regina, Regina, SK S4S 0A2, Canada
2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China |
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| Abstract: | The Jinding Zn-Pb deposit has been generally considered to have formed from circulating
basinal fluids in a relatively passive way, with fluid flow being controlled by structures and sedimentary
facies, similar to many other sediments-hosted base metal deposits. However, several recent studies have
revealed the presence of sand injection structures, intrusive breccias, and hydraulic fractures in the open
pit of the Jinding deposit and suggested that the deposit was formed from explosive release of overpressured
fluids. This study reports new observations of fluid overpressure-related structures from underground
workings (Paomaping and Fengzishan), which show clearer crosscutting relationships than
in the open pit. The observed structures include: 1) sand ( rock fragment) dikes injecting into fractures
in solidified rocks; 2) sand ( rock fragment) bodies intruding into unconsolidated or semi-consolidated
sediments; 3) disintegrated semi-consolidated sand bodies; and 4) veins and breccias formed from
hydraulic fracturing of solidified rocks followed by cementation of hydrothermal minerals. The development
of ore minerals (sphalerite) in the cement of the various clastic injection and hydraulic fractures
indicate that these structures were formed at the same time as mineralization. The development of
hydraulic fractures and breccias with random orientation indicates small differential stress during mineralization, which is different from the stress field with strong horizontal shortening prior to mineralization.
Fluid flow velocity may have been up to more than 11 m/s based on calculations from the size
of the fragments in the clastic dikes. The clastic injection and hydraulic fracturing structures are interpreted
to have formed from explosive release of overpressured fluids, which may have been related to
either magmatic intrusions at depth or seismic activities that episodically tapped an overpressured fluid
reservoir. Because the clastic injection and hydraulic structures are genetically linked with the mineralizing
fluid source, they can be used as a guide for mineral exploration. |
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| Keywords: | Hydrodynamics Clastic injection Hydraulic breccia Hydraulic fractures Jinding Fluid overpressure |
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