Characterisation and prediction of sediment-hosted ore deposits using sequence stratigraphy

The processes that form stratabound ore deposits involve diagenesis, fluid-flow, rock–fluid interaction and metal fixation which, like the maturation, migration and entrapment of hydrocarbons are integral aspects of basin history. Sequence stratigraphy is a method by which the stratigraphic record of sedimentary basins may be analyzed and placed in facies-dependant depositional units related to changes in relative sea level. Here we show how some of the concepts of sequence stratigraphy can be applied in the interpretation and better understanding of known metal generative zones and in the prediction of potential host rocks of sedimentary ore deposits. Sequence stratigraphic concepts are of most use in explaining and predicting the juxtaposition of metal- or sulphur-generative sediments such as evaporites, red-beds and organic-rich shales, and in understanding mineralization associated with black shales, hardgrounds and reworking surfaces (placer deposits). The analysis of depositional sequences may also enable predictions to be made concerning likely ore-hosts, such as MVT mineralization in carbonate reefs and reservoir sands. The final position of a sedimentary ore deposit is dependent on (1) the geometry of the sedimentary sequence, (2) the depositional environments (i.e. specific lithologies) within each systems tract, and (3) the structure of the basin. We test this model by creating a sequence stratigraphic model for the Precambrian Aberfeldy barite deposit of Scotland and then consider other horizons in the Dalradian succession that may also stratiform mineral deposits.