Ref.: Brobst, D.A. (1958), Barite Resources of the United States, USGS Bull. 1072-B: 80 (Table 9), 85-86; Olson and others (1954); Zadra and others (1952).
The Mountain Pass District contains one of the largest single concentrations of barite in the world. The barite occurs in veins with rare-earth minerals.
The Mountain Pass District is in a block od metamorphic rocks of Precambrian age. The rocks are gneisses, schists, migmatites, granitic pegmatites and small amounts of foliated mafic rocks. The block is bounded on the north by a fault, on the east and south by alluvium of the Ivanpah Valley, and on the west by the Clark Mountain normal fault that brings volcanic and sedimentary rocks of Paleozoic age into contact with rocks of Precambrian age.
The vein deposits are related to several large intrusive bodies and several hundred thin dikes of potash-rich rocks of probable Precambrian age that cut the metamorphic complex. The composition of these igneous rocks ranges from biotite shonkinite through syenite to granite. The granitic rocks generally appear to be the youngest and the shonkinites the oldest in the cycle of intrusion. Rare earths and barite are most abundant in and near the SW side of the largest shonkinite-syenite body, which is about 6,300 feet long. Most of the 200 carbonate-rich veins mapped by Olson and others are less than 6 feet thick, but one large body of carbonate rock near the Sulphide Queen Mine is 2,400 feet long and has an average width of 400 feet. This large body has more than 10 times the exposed area of all the other veins combined.
The bulk composition of the ore is about 20% barite, 60% carbonate minerals (calcite, dolomite, ankerite, and siderite), 10% RRE-bearing fluocarbonate minerals (chiefly basnäsite), and 10% quartz and silicates.
