Abstract: Temporal-spatial association between Tertiary lamprophyre dykes and epithermal Au-Ag mineralization in Sonora, northwestern Mexico

Lamprophyres are mafi c to intermediate volatile-rich igneous rocks that occur mainly as dykes and are often been associated with metallic (mainly Au) ore deposits. Although clearly in most cases the relationship between the lamprophyres and the mineralization is not genetic, there are numerous cases where there exists a spatial and/or temporal relationship between them. The present work focuses on the petrology and geochronology of the lamprophyre dykes of the Hermosillo area, Sonora, northwestern Mexico comparing their age and genesis to that of known Au-Ag ore deposits in the region. In Sonora, the lamprophyres commonly crosscut the 90–40 Ma Sonoran batholith; however, they have also been observed in hydrothermal gold deposits in the north-central and northwestern portions of the State. In the Hermosillo area the dykes vary in width from about 10cm to as much as 5m. They vary in mineralogy from hornblende-phyric spessartite to phlogopite-phyric kersantite, which have medium-K calc alkaline and shoshonitic affi nities respectively. In the area of study 40Ar/39Ar geochronology for the lam-