The prospecting strategy for a deep Cu-Ag ore deposit in Poland – An anatomy of success

[Display omitted] •3 Deep Kupferschiefer Cu-Ag deposits has been recently discovered in SW Poland.•Successful prospecting strategy included reprocessing of archival geological data.•Organic matter parameters were effective indicators of high-grade ore.•New deposits display some differences comparing to known shallow deposits in Poland.•Pre-feasibility studies showed mining will be profitable using modern technologies. The article presents the prospecting strategy implemented by Miedzi Copper Corporation in search for new Cu-Ag ore deposits of the Kupferschiefer type. Sediment-hosted stratiform copper deposits in Poland occur mostly in the Fore-Sudetic Monocline, in the contact zone between the continental red beds (Rotliegend) and Zechstein marine sediments. The ore-bearing series consists of white sandstone (Weissliegend), copper-bearing shale (Kupferschiefer) and carbonates (Zechstein Limestone). The southern-central part of the Fore-Sudetic Monocline is a well-known Lubin-Sieroszowice mining area, where mining operations are conducted at the depths up to 1300 m below surface. However, due to significant depletion of shallower reserves, deep Cu-Ag mineralisation have recently become a subject of interest. Several basic problems had to be resolved in order to reach for such deposits: finding indicators suggesting the presence of rich mineralisation; more precise identification of the current geothermal field in the area of the Fore-Sudetic Monocline; and the availability of modern technologies which would allow safe and economic operation of a deep underground mine. In 2011, Miedzi Copper Corporation initiated its exploration programme focused on deep Cu-Ag ore deposits, based on known prognostic areas in the vicinity of palaeorises and contacts between oxidised and reduced facies, as copper mineralization occurs at the rims of oxidised areas, on the reduced side of the redox boundary. Exploration programme has led to the documentation of three new deep deposits: Nowa Sól, Sulmierzyce North and Mozów, two of which were identified in areas previously described as prospective by the Polish Geological Institute.