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Upcoming TALKS |
Title: Targeting sulphide mineralisation using Sedimentary corrected Regional Gravity by AEM in the Iberian Pyrite Belt Date: Tuesday April 9th at 12:00 PM EST Speaker: Isla Fernández-Senior Geophysicist, lecturer in the Master of Mineral Resources at UNIA, teaching the subject of Geophysics. Location: Virtual, please register here Abstract: Gravity surveys have long been a fundamental exploration tool in the Iberian Pyrite Belt. Stephen M. McIntosh Joseph P. Gill Andrew J. Mountford (1999) showed Las Cruces to align with a 2.9 mGal anomaly. Similarly, Leca (1990) showed Neves and Corvo to each align with a >0.5 mGal anomaly. Unfortunately, dense surrounding volcanics add to the gravity field, whilst unconformably overlying post mineral sedimentary cover and oxidation subtracts from it. To improve interpretation of the gravity field, a Sedimentary-cover-thickness correction is proposed and tested in this paper. The Sedimentary cover is known to be lower density and higher conductivity than the basement and host rocks. Forward modelling shows a typical thickness of Sedimentary can have a 0.5 mGal response. It is also well known that AEM can map the top-of-basement quite accurately (Viezzoli et al., 2020). In this paper, we establish a method to estimate depth-to-top of basement from AEM, corrected by drilllogs, and employing a suitable density for the sedimentary cover. The sedimentary-cover-correction is then subtracted from the regionally corrected Bouguer Anomaly. This work would help to discriminate gravity anomalies created by palaeo-relief, from anomalies caused by bedrock sulphides beneath a cover layer of lower density, but also to locate possible deposits, with greater depth resolution, giving more confidence in drilling deeper low-amplitude gravity anomalies. Mapping the sedimentary cover will reduce the number of drillholes targeting anomalies due to sedimentary depth variations. This method is then applied to a levelled regional gravity dataset. Misleading results caused by deeper weathering of exposed basement are also identified using mapped geology, satellite imagery, and aerial photography. The result is a Bouguer Anomaly map as it would have looked pre-Tertiary. Author Biography: Isla Fernández-Senior Geophysicist, has more than 26 years of experience working as a geophysicist in mining exploration, developing her work in direct contact with geologists, being one of her main skills the integration of geology and geophysics in exploration projects. Since 2017 he has participated in 3 European research projects in the field of mining exploration, in all of them leading the tasks related to geophysics. Since 2011 she is a lecturer in the Master of Mineral Resources at UNIA, teaching the subject of Geophysics. Upcoming Talks: TBD
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