A two-way approach for the definition of anthropogenic and natural copper anomalies at a massive sulphide mine. The case of the Neves Corvo mine in Iberian Pyrite Belt, Portugal

The Neves Corvo mine is situated in a very important massive sulphide metallogenic province, the Iberian Pyrite Belt (IPB). The study area includes this copper mine and six other abandoned Cu, Mn and pyrite mines. The objective of the study was to distinguish pre-mining concentrations of Cu from mining sources. This was done to evaluate the real extension of mining induced copper in soils. To decrease costs in the remediation stage, by means of the presented approach, the mining induced Cu in the environment will be separated from its pre-mining baseline concentration.The mathematical approach used is based on two regressions with two distinct sets of soil samples (surface horizon) collected in the same locations in different periods (campaigns). One set of soil samples was collected before the existence of the Neves Corvo mine in the 1970 decade (1st campaign) and the other set was sampled in 1998, ten years after Neves Corvo mining began (2nd campaign). Regressions were made independently, with samples from the two sets: one with a group of samples selected from the 1st campaign, in an area where no mining activity was known, and the second regression was performed with all the samples of the 2nd campaign set.From the first regression, the tests proved that it was possible to distinguish mining induced copper concentrations from the pre-mining baseline copper values. The second regression resulted not suitable for the objective because the independent variables were not appropriate for the tests and probably the complete set of samples of the second campaign was also not appropriate. This study establishes areas where Cu concentrations were possibly only prior to mining and others, which were mining induced.

► First regression distinguishes copper concentrations that can be mining induced from the pre-mining copper.
► Second regression independent variables were not suitable for the objective.
► Areas where Cu in soils is only parent material originated, and others, which were mining induced are defined.