New Mexico Mineral Symposium — Abstracts

The Quitman Mountains-Sierra Blanca igneous complex (QMSB) consists of a diverse package approximately 200 km2 of mid-Oligocene volcanic, granitic, and metamorphic lithologies, which are reasonably well exposed adjacent to Interstate 10.

This mineralization study is part of a detailed petrological and geochemical investigation of the QMSB complex, involving more than 250 whole-rock geochemical analyses and 270 electron microprobe analyses of selected mineral phases.
To a first approximation, mineralization types in the QMSB complex can be grouped on a spatial and temporal basis into three general categories:

1. skarn type. This represents the earliest mineralization in the complex, with capricious amounts of W-Mo, Pb-Zn-Ag, and Be¬Sn-Fe F-(±Ba±Bi±Cu±Nb±Se±Zr±REE). The mineralogy is predominantly an amphibolite facies garnet-magnetite skarn with minor hornfels. It consists of variable amounts of andradite, grossular, magnetite, calcite, epidote, quartz, diopside, wollastonite, vesuvianite, hematite, graphite, fluorite, pyrite, actinolite, tremolite, helvite, nontronite, phenakite, pyrophyllite, wavellite, adularia, chrysocolla, and scheelite. This type of mineralization formed from the ring-fracture intrusion of calc-alkalic to alkalic granitoid rocks with metaluminous phases ranging from diorites, quartz monzonites, syenites to pegniatites. The chemistry of these granitoid rocks together with the older co-magmatic volcanic rocks is suggestive of A-type magmatism (anhydrous, anorogenic, and somewhat alkaline). Crystallization-temperature estimates vary from 620°C to 780°C with f(0)2 at -18. A rare-metal mineralization type is manifested in the pegmatite phase with anomalous amounts of Li¬Nb-Ta-Zr-U-Th-Hf-REE. Crude metasomatic-zoning effects are apparent in the skarn as shown by progressive rare-metal and REE enrichment in some of the calcic endoskarns. At the southeastern limit of the complex there are zones of banded Be-Sn-Fe-F mineralization, which are analogous to Australian "wrigglite" skarns.
2. rhyolite-ongonite type. F-Be-U-Sn-(±Cs±Li±Sb±Ta±Tl) minerali¬zation occurs with the high-silica rhyolites in the laccoliths of the Sierra Blanca Peaks. These rhyolites are akin to other mineralized ongonites and topaz rhyolites. The mineralization is mainly fluorite with minor occurrences of beryl and cassiterite and more rare occurrences of gearksutite, ralstonite, and thomsenolite.
3. hydrothermal-vein type. This is extensive throughout most of the QMSB complex and is the latest mineralizing episode. It is intimately associated with the closing stages of a resurgent caldera complex in the northern Quitman Mountains. Pb-Zn-Ag¬(±Cu±U±Au?), Fe-Mo, F, and Ba veinings occur in a preferred east-northeast trend. These veins are also superimposed on the skarns resulting in a scanty, retrograded (to greenschist facies) zonation of actinolite, tremolite, calcite, quartz, sericite, and hematite.

Mineralization has been recorded in these veins showing variable and limited ore extent with minor amounts of pyrite, argentiferous galena, sphalerite, chalcopyrite, barite, molybdenite, magnetite, hematite, siderite, goethite, cerrusite, wulfenite, greenockite, torbernite, limonite, calamine, pyromorphite, psilomelane, and chrysocolla. Gangue minerals typically are quartz and calcite with more rare occurrences of tourmaline (schorl variety).