title: Assessing the Potential for Magmatic Sulfides within Southwestern Laurentia Large Igneous Province
Creators: name: Boes, Thomas
Publisher: name: University of Nevada, Las Vegas
publisherIdentifier: https://ror.org/0406gha72
publisherIdentifierScheme: ROR
Year: 2024

description: The ~1.1 Ga magmatism of the Southwestern Laurentia Large Igneous Province (SWLLIP) generated a series of mafic-ultramafic sheets, sills, and dikes emplaced within Mesoproterozoic sedimentary units and older crystalline basement rock throughout the southwest United States and northern Mexico. This large igneous province (LIP) event remains enigmatic in identifying the processes that generated this magmatism. In addition, potential links to the contemporaneous magmatism of North America's magmatic Ni-Cu-platinum group element (PGE) mineralized Mid-Continent Rift (MCR) LIP to the northeast of the SWLLIP remain unclear. The contemporaneous 1.1 Ga MCR LIP event hosts economically viable magmatic sulfide deposits in the Duluth Complex in Minnesota and elsewhere, providing further incentive to understand the links between the LIP events as well as independently assessing the mineral exploration potential for magmatic sulfide deposit formation within the SWLLIP. This study aims to further our knowledge of the petrogenesis of the SWLLIP and the potential of this magmatic event to host magmatic sulfide mineralization.</p><p>Whole-rock geochemical and Pt, Pd, and Au data have been obtained for 52 SWLLIP samples from California, Arizona, and New Mexico, allowing an initial assessment of the petrogenesis, magmatic sulfide fertility, sulfide saturation status, and crustal contamination of magmas of the SWLLIP to be assessed. All these factors are critical in determining the potential for this LIP to host magmatic Ni-Cu-PGE sulfide mineralization. Two suites have been identified within the SWLLIP that define two distinct magmatic pulses during the LIP event: a potentially prospective (from a magmatic sulfide viewpoint) tholeiitic suite and a seemingly unprospective alkaline suite. The tholeiitic suite has undepleted chalcophile element samples, demonstrating that the magmas that formed the suite were derived from a fertile mantle source region with sufficient partial melting to generate chalcophile-undepleted magmas. Furthermore, some tholeiitic samples within this suite are depleted in chalcophile elements and are crustally contaminated, suggesting that the magmas assimilated country rocks and became sulfur-saturated before emplacement. This process is crucial in most magmatic Ni-Cu-PGE mineralizing systems elsewhere and within the SWLLIP-generated immiscible sulfide melts deposited elsewhere within the system. This indicates the magmatic sulfide prospectivity of intrusions with this tholeiitic suite within the SWLLIP. In comparison, alkaline SWLLIP suite samples are uniformly depleted in chalcophile elements and display varying degrees of crustal contamination that do not contain sufficient sulfides, inferring they are unfertile. These unfertile melts were generated by low degree partial melting of the mantle and did not become sulfur saturated before emplacement. Overall, this research indicates that exploration for magmatic sulfides within the SWLLIP should focus on intrusions and sections of the LIP with affinities to the tholeiitic suite. The transitional alkaline suite is likely unprospective of chalcophile elements from an exploration viewpoint. This geochemical dataset allows for comparison between the two distinct pulses of magmatism in the SWLLIP and the MCR magmatism, particularly the mafic magmatism associated with the Duluth Complex, which is suggestive of a single plume under the North American craton.