In situ magnetic susceptibility and gamma radiation data in the Candela-Monclova intrusive belt, Northeast Mexico: case studies of the Cerro Colorado and Cerro Marcelinos plutons

Abstract

The Cerro Marcelinos (CM) and Cerro Colorado (CC) plutons are part of the Candela-Monclova intrusive belt (NE Mexico), which is mid-Eocene in age (43-35 Ma). It intrudes into the Sabinas Basin, primarily made up of limestones, of Lower and Upper Cretaceous age. Around several intrusions, including the CM and CC plutons, mineralizations are known. However, how much hidden mineralizations would occur is not known. Trends within the plutons and in contact aureoles are also poorly described at present. Therefore, we provide here in situ magnetic susceptibility (MS) and gamma ray spectrometry (GS) data along two composite transects, one in each pluton, to delineate such potential trends. The data show variations of 0.003 × 10-3 SI and 104 × 10-3 in MS and of 7.1 nGy/h and 196 nGy/h in GS with a clear relation to rock type and amount of metasomatism. The radioactive contents in the outcrops of contact metamorphic rocks indicate a contact metasomatism with differing degrees of alteration during emplacement of the plutons. The host limestones have magnetic minerals incorporated during the intrusion process. MS and GS indicate an increase in the degree of acidity towards the center of both plutons, possibly associated with the later stages of the magmatic differentiation process. The MS could divide the igneous rocks into two groups, weakly magnetic (group 1 with MS ≤ 3 × 10-3 SI) and strongly magnetic (group 2 with MS > 3 × 10-3 SI), associated with the magnetite and ilmenite series, respectively. These classes provide useful information regarding the internal magnetic zoning in the plutons, which can be associated with mineralizations of mainly Au and Cu. Mainly, the magnetite series (group 2) delimited more perspective zones for mineral exploration. This zoning in MS could guide future mineral exploration in both plutons.