Rob Davidson continued his PhD research on the sediment-hosted San Sebastian intermediate sulfidation epithermal vein system in Durango, Mexico, in 2019 with support from Hecla Mining. His research aims are to: determine the relationship between the vein systems and occurrences within the San Sebastian district; characterise the Mesozoic sedimentary host rock lithologies; understand the structural controls on vein formation; characterise whole rock and trace element geochemistry of veins, vein stages, host rock, volcanic rocks, and alteration in order to develop potential vectors towards mineralisation; and date, using a range of geochronological methods, the veins, host rocks and alteration.

Research focussed on the samples and observations collected during his 2019 fieldwork, including observation of the veins underground in order to test structural observations from the 3D interpretation of geology and structure, and to compare textural and paragenetic observations to those made from core. Visual inspection of the host rocks at San Sebastian can readily distinguish two types of alteration: near surface weathering, and at depth, a broad volume of hardened and bleached mudstone. Staining with sodium cobaltinitrite indicates that this bleaching alteration is dominated by K-feldspar. It also reveals a third alteration domain spatially related to the main veins and which overprints the broader potassium alteration. Thus, there are three alteration events recognised at San Sebastian: 1) a pre-mineral broad event dominated by K-feldspar flooding; 2) syn-mineral vein-related alteration; and 3) post-mineral weathering.

Further analyses of hand sample descriptions, polished thin section descriptions, SEM analyses of mineralisation, potassium feldspar staining, SWIR (TerraSpec) data collection, pXRF (Olympus Vanta) data collection, a carbon and oxygen (in carbonates) isotope study, a pilot Raman geo-thermometry study of the host rocks, and age dating of the regional volcanic rocks and hydrothermal alteration, are continuing. Rob presented a poster of his initial findings at the SEG Conference in Santiago in October. A third and final field season is planned for March 2020.

Rob Davidson continued his PhD research on the San Sebastian intermediate sulfidation epithermal vein system in Durango, Mexico, in 2018. His research aims are to: determine the relationship between the vein systems and occurrences within the San Sebastian district; characterise the Mesozoic sedimentary host rock lithologies; understand the structural controls on vein formation; characterise whole rock and trace element geochemistry of veins, vein stages, host rock, volcanic rocks, and alteration in order to develop potential vectors toward mineralisation; and date, using  a range of geochronological methods on the veins, host rocks and alteration.

While not the only Mexican epithermal deposit hosted within Mesozoic sediments, there is a lack of published research addressing the alteration footprints that these types of systems leave within sedimentary rocks. Research was focussed on the samples collected during his 2017 fieldwork, and included an initial 3D structure and geology interpretation, hand sample descriptions, polished thin section descriptions, SEM analyses of mineralisation, potassium feldspar staining, SWIR (Terraspec) data collection, pXRF (Olympus Vanta) data collection, a carbon and oxygen (in carbonates) isotope pilot study and initiation of age dating of the regional volcanic rocks. These analytical techniques will be applied to a set of 1,502 samples from diamond drill core and RC chips systematically collected along five representative cross-sections roughly 500 metres apart. A second field season is planned for early 2019.

Rob Davidson has begun his PhD research on the San Sebastian intermediate sulfidation epithermal vein system in Durango, Mexico. His research aims are to: determine the relationship between the vein systems and occurrences within the San Sebastian district, characterise the host rock sequence lithologies and controls on vein development, understand the structural controls on vein formation, characterise whole rock and trace element geochemistry of veins, vein stages, host rock, volcanic rocks, and alteration in order to develop potential vectors toward mineralisation, and date, using a range of geochronological methods, veins, vein stages, host rock, volcanic rocks and alteration.

This research is supported by Hecla Mining over a three-and-a-half-year period. Rob undertook fieldwork between October and December; he will start to carry out analysis of his findings in 2018, followed by further fieldwork.