Water-rock interactions: the formation of an unusual mineral assemblage found in a Siberian coal

Leah N Thompson,Sergey I Arbuzov,Robert B Finkelman,O Chudaev,R Harmon,Y Kharaka,R Millot,O Shouakar-Stash

doi:10.1051/e3sconf/20199801050

Leah N Thompson, Sergey I Arbuzov + Show 6 more

Open Access

https://doi.org/10.1051/e3sconf/20199801050

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Abstract

Volcanic ash is regularly found in coal and is particularly common in the Minusinsk coal basin in southern Siberia, Russia. Ash deposits in coal are usually observed in the form of thinly bedded, kaolinite-rich layers called tonsteins. The coal we studied by scanning electron microscopy with an energy dispersive detector contained many of the minerals typically found in tonsteins: kaolinite groundmass, volcanogenic phenocrysts such as K-feldspar, quartz, apatite, and zircon, along with secondary minerals such as galena, sphalerite, and REE minerals. However, in addition to these commonly observed minerals, the groundmass contains a rare calcium-bearing magnesian siderite in roughly equal proportion to the kaolinite. Ca-Mg siderite has only been reported in a few Australian coals and never at these relatively high proportions. The relative levels of K-feldspar, apatite, and quartz are consistent with a parent magma of felsic to intermediate composition. The Ca-rich-Mg siderite appears to have developed late in the diagenetic process, likely as a result of the dissolution of calcic feldspars, micas, and mafic minerals in the acidic peat waters releasing calcium, iron, and magnesium which reacted with carbon dioxide from the decomposing plant matter.

Highlights

Altered volcanic ash is commonly found in coals throughout the world [1, 2]
Layers of altered volcanic ash are common in the Minusinsk coal basin in southern Siberia, Russia
The Minusinsk coal basin is located in an intermountain trough of the same name

Summary

Introduction

Altered volcanic ash is commonly found in coals throughout the world [1, 2]. The ash deposits in coal are usually observed in the form of thinly bedded, kaolinite-rich layers called tonsteins. Layers of altered volcanic ash are common in the Minusinsk coal basin in southern Siberia, Russia. The Minusinsk coal basin is located in an intermountain trough of the same name. There are four independent coal deposits within the basin: Chernogorskoe, Beiskoe, Izykhskoe, and Askizskoe deposits. More than 40 tonsteins were found in the coal seams of the Beiskoe deposit [3]. For this preliminary investigation we selected several volcanic ash layers from coal bed 19a.

Observations

Interpretation of water-rock interactions