Young orogenic gold mineralisation in active collisional mountains, Taiwan
Journal
Mineralium Deposita
Journal Volume
45
Journal Issue
7
Pages
631-646
Date Issued
2010
Author(s)
Abstract
Gold-bearing vein systems in the high mountains of Taiwan are part of the youngest tectonic-hydrothermal system on Earth. Tectonic collision initiated in the Pliocene has stacked Eocene-Miocene marine sedimentary rocks to form steep mountains nearly 4 km high. Thinner portions of the sedimentary pile (~5 km) are currently producing hydrocarbons in a fold and thrust belt, and orogenic gold occurs in quartz veins in thicker parts of the pile (~10 km) in the Slate Belt that underlies the mountains. Metamorphic fluids (2-5 wt.% NaCl equivalent) are rising from the active greenschist facies metamorphic zone and transporting gold released during rock recrystallisation. Metamorphic fluid flow at the Pingfengshan historic gold mine was focussed in well-defined (4 km3) fracture zones with networks of quartz veins, whereas large surrounding volumes of rock are largely unveined. Gold and arsenopyrite occur in several superimposed vein generations, with ankeritic alteration of host rocks superimposed on chlorite-calcite alteration zones as fluids cooled and became out of equilibrium with the host rocks. Mineralising fluids had δ18O near +10‰, δ13C was between -1‰ and -6‰ and these fluids were in isotopic equilibrium with host rocks at ~350°C. Ankeritic veins were emplaced in extensional sites in kink fold axial surfaces, formed as the rock mass was transported laterally from compressional to extensional regimes in the orogen. Rapid exhumation (>2 mm/year) of the Slate Belt is causing a widespread shallow conductive thermal anomaly without igneous intrusions. Meteoric water is penetrating into the conductive thermal anomaly to contribute to crustal fluid flow and generate shallow boiling fluids (~250°C) with fluid temperature greater than rock temperature. The meteoric-hydrothermal system impinges on, but causes only minor dilution of, the gold mineralisation system at depth. © 2010 Springer-Verlag.
Subjects
Gold; Hydrothermal; Mesothermal; Metamorphic fluid; Meteoric water; Taiwan
SDGs
Other Subjects
collision zone; gold; hydrothermal system; metamorphism; meteoric water; mineralization; ore deposit; orogeny; quartz vein; temperature anomaly; Taiwan
Type
journal article