Pb-Rich Slags, Minerals, and Pollution Resulted from a Medieval Ag-Pb Smelting and Mining Operation in the Silesian-Cracovian Region (Southern Poland)

Jerzy Cabała,Eligiusz Szełęg,Dariusz Rozmus,Rafał Warchulski,Dorota Środek

doi:10.3390/min10010028

Abstract

Since the 12th century in the Silesian-Cracovian area, lead, litharge, and silver have been produced by the pyrometallurgical processing of Pb-Ag-Zn ore. Slags and soils contaminated with heavy metals (Zn, Pb, Cd, Fe, Mn, As) were the subject of this research. Samples were collected during archaeological works in the area of early medieval metallurgical settlement. The main goals of the analyses (Scanning Electron Miscroscopy-Energy Dispersive Spectroscopy (SEM-EDS), Electron Probe Microanalyzer (EPMA), X-ray diffraction (XRD), Atomic Absorption Spectroscopy (AAS)) were the determination of the mineralogical composition of furnace batches and smelting temperatures and conditions. In soils, the anthropogenic phases enriched in Pb, Zn, Fe, Mn, P, and primary minerals like goethite, ferrihydrite, sphalerite, galena, smithsonite, minrecordite, cerussite, gypsum, anglesite, jarosite, and hemimorphite were identified. The soil from former metallurgical settlements contained up to 1106 mg·kg−1 Pb, 782 mg·kg−1 Zn, 4.7 mg·kg−1 Cd in the fine fraction. Much higher heavy metal concentrations were observed in the waste products of ore rinsing, up to 49,282 mg·kg−1 Pb, 64,408 mg·kg−1 Zn, and 287 mg·kg−1 Cd. The medieval smelting industry and Pb-Ag-Zn ore processing are marked by highly anomalous geochemical pollution (Pb, Zn, Cd, Fe, Mn, Ba) in the topsoil. The methods of mineralogical investigation, such as SEM-EDS or EMPA, can be used to identify mineralogical phases formed during metallurgical processes or ore processing. Based on these methods, the characteristic primary assemblage and synthetic phases were identified in the area polluted by medieval metallurgy and mining of Pb-Ag-Zn ores, including MVT (Mississippi Valley Type) deposits. The minerals distinguished in slags and the structural features of metal-bearing aggregates allow us to conclude that batches have included mostly oxidised minerals (PbCO3, ZnCO3, CaZn(CO3)2, FeOOH), sulfides (PbS and ZnS) and quartz (SiO2). The laboratory experiment of high-temperature heating of the examined slags showed that smelting temperatures used in the second half of 13th century were very high and could have reached up to 1550 °C. The results indicate, that geochemical and mineralogical methods can be used to obtain important information from archaeological sites, even after archaeological work has long ceased.

Highlights

In medieval Europe, the development of countries and power centres was often connected with the sourcing and utilization of mineral resources
The results indicate, that geochemical and mineralogical methods can be used to obtain important information from archaeological sites, even after archaeological work has long ceased
The main goal of this research was proving if scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), electron-probe microanalyser (EPMA), or X-ray diffraction (XRD) results obtained from material collected at previously investigated archaeological sites could be useful for analysing the input material type, metallurgical methods, and degree of environmental pollution

Summary

Introduction

In medieval Europe, the development of countries and power centres was often connected with the sourcing and utilization of mineral resources. The proximity of iron, gold, silver, lead, copper and tin deposits has promoted the development of Minerals 2020, 10, 28; doi:10.3390/min10010028 www.mdpi.com/journal/minerals. In the period between the 10th and 12th centuries, iron, lead, tin, silver, and gold had become more important for the development of civilization in Central and Eastern European countries. Since the beginning of the 10th century in medieval Europe, in areas where ores of Ag-Pb, Au, As-Au, Cu, Sn and Fe occurr, mining centres have appeared, such as at the Ore Mountains (Erzgebirge), Harz Mountains, and Sudetes. The deposit’s location has been advantageous for the development of the silver and lead mining in the 12th century, which is confirmed by historical sources and archaeological research [3]

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