Two-stage fluid pathways generated by volume expansion reactions: insights from the replacement of pyrite by chalcopyrite

Yang Zhang,Yuanfeng Cai,Lixin Gu,Yang Qu,Gaojun Li,Qin Wang

doi:10.1038/s41598-020-76813-9

Abstract

Volume expansion reactions involved in mineral–fluid interactions are linked to a number of geological processes, including silicate weathering, retrograde metamorphism, and mineralization. However, the effect of volume expansion on replacement reactions remains unclear. Here, we demonstrate that reactions associated with volume expansion during the replacement of pyrite by chalcopyrite involve two competing processes. The reaction is initially augmented because of the development of reaction-induced fractures in the pyrite. However, these fractures are subsequently filled by compacted products, which ultimately disrupts the contact and interaction between bulk fluids and the pristine pyrite surface. These competing processes indicate that replacement reactions are both augmented and inhibited by volume expansion reactions during pyrite replacement.

Highlights

Volume expansion reactions involved in mineral–fluid interactions are linked to a number of geological processes, including silicate weathering, retrograde metamorphism, and mineralization
Volume expansion reactions have a significant impact on the rate of fluid–mineral interactions that occur in a number of settings, including retrograde metamorphism during exhumation of high-pressure and ultrahighpressure metamorphic rocks[1,2,3], chemical weathering of silicate minerals[4,5], peridotite serpentinization[6,7], and hydrothermal mineralization[8,9,10]
We investigate the replacement of pyrite by chalcopyrite under controlled conditions to study the rate of the replacement reaction in response to volume expansion, which is a type of volume-increasing r eaction[19]

Summary

Introduction

Volume expansion reactions involved in mineral–fluid interactions are linked to a number of geological processes, including silicate weathering, retrograde metamorphism, and mineralization. The reaction is initially augmented because of the development of reactioninduced fractures in the pyrite These fractures are subsequently filled by compacted products, which disrupts the contact and interaction between bulk fluids and the pristine pyrite surface. These competing processes indicate that replacement reactions are both augmented and inhibited by volume expansion reactions during pyrite replacement. We investigate the replacement of pyrite by chalcopyrite under controlled conditions to study the rate of the replacement reaction in response to volume expansion, which is a type of volume-increasing r eaction[19] This replacement reaction was chosen for the following reasons: (1) pyrite crystals can be collected and cut into specific shapes; (2) the rapid transformation at 200 °C allows observation on a laboratorial timescale; and (3) the simple compositions of pyrite and chalcopyrite eliminate the influence of chemical changes during hydrothermal experiments

Methods

Results

Conclusion