PETROGRAPHY AND HXRF GEOCHEMISTRY OF VOLCANIC AND VOLCANICLASTIC UNITS AND ASSOCIATED DIKES IN THE KNIGHT RANGE, GRANT COUNTY, SOUTHWESTERN NEW MEXICO

Unmapped, intermediate to mafic, magnetite-rich rocks are associated with a northeast-dipping package of Cretaceous-Tertiary sedimentary, volcanic, and volcaniclastic units that make up the Knight Range of Grant County in southwestern New Mexico. The Knight Range is located at the southern edge of the Mogollon-Datil volcanic field and the northern edge of the southern Basin and Range province. The volcanic and volcaniclastic rocks unconformably overlie the Mesoproterozoic Burro Mountain Granite, which is intruded by Mesoproterozoic diabase dikes that contain a significant (~12%) component of magnetite and ilmenite. The unmapped magnetite-rich rocks are found cross-cutting the Cretaceous-Tertiary Conglomeratic Sandstone of Knight Canyon (TKk) and associated with the Latite and Andesite of Malpais Hills (Tml). Hypotheses for the origin of these magnetite-rich units include relationships with 1) mapped “Mesoproterozoic” diabase dikes, 2) the Andesite of JPB Mountain (Tja), which also contains magnetite, or 3) the unit Tml; an alternative hypothesis is that 4) later metasomatism produced similar magnetite content in these unrelated units. To address the origin of the magnetite-rich rocks, samples of these and other units in the Knight Range have been collected and will be described petrographically. In addition, the magnetite-bearing units will be geochemically analyzed using a handheld XRF (hXRF). Any genetic relationships that might be identified based on geochemistry could have implications for the relative ages of units in the Knight Range or for the source of the Andesite of JPB Mountain. This work may also contribute to the understanding of the relationships between these rocks and the regional history of the Laramide orogeny, ignimbrite flare-up and related mineralization, and Basin and Range extension.