Discovery of the Magdalena ore body. The leading role of geophysical methods for the exploration of a deep volcanogenic massive sulphide deposits (VMS) in the Iberian Pyrite Belt

Abstract

The Magdalena volcanogenic massive sulphide (VMS) deposit, located in the province of Huelva (Spain) and discovered by Minas de Aguas Teñidas S.A.U. (MATSA) in 2013 constitutes the largest discovery to be made in the Iberian Pyrite Belt (IPB) in recent decades. During a first phase of exploration, the deposit was discovered by drill testing a conductivity anomaly that was first detected during an airborne (helicopter) transient electromagnetic survey (VTEM) in 2011. Drill-hole MA-01 intersected the massive sulphide body at a depth of between 225 m and 248 m. Throughout the drilling campaign of the sulphide body later named “Masa 1”, the drill holes were surveyed using Downhole TEM and Mise-à-la-Masse geophysical methods and during this work the Downhole TEM results from drill hole MA-21, which was originally drilled to 320 m, detected the presence of a deeper and larger sulphide body. The appearance of an off-hole, down-hole TEM anomaly in hole MA-21 was fundamental in the discovery of “Masa 2” which was made once the drill rig was recollared on the original MA-21 pad and drilled to a depth of 530 m. This second sulphide lens (“Masa 2”) was not detected by the initial VTEM survey because it was beyond the range for the system and was subsequently drill tested at depths between 350 and 1,000 m. The discovery of the Magdalena deposit has demonstrated the crucial role of certain geophysical methods for the detection of deep VMS deposits and confirms the prospectivity of the IPB as a metallogenic area of undoubted potential as far as the existence of similar deposits are concerned.