Shirokaya Valley, Lake Baikal area, Irkutsk Oblast, Russiai

Regional Level Types
Shirokaya Valley	Valley
Lake Baikal area	Mineral Occurrence Area
Irkutsk Oblast	Oblast
Russia	Country

The Ust’-Krestovsky complex of gabbro is composed of high-Ti and high-alkaline Ti-fassaite monzogabbro, pyroxenite, and nepheline-Ti augite rocks (phase 1) and phlogopite monzogabbro (phase 2), often altered to amphibolite and gneiss, with moderate Ti contents. The rocks of phase 1 form several small bodies along the sides of the Krestovsky Valley and are related to high-temperature pyroxene hornfels after the Birkhin porphyrite. Phase 2 rocks occur as part of the Ust’-Krestovsky intrusion within the Krestovsky Valley (Figure 4) and local dikes in marble. They are compositionally similar to subalkaline metagabbro in the Tazheran Massif and composite mafic dikes in northern Olkhon areas [18]. The Ust’-Krestovsky gabbro samples likewise bear suprasubduction signatures but differ from the Birkhin volcanoplutonic rocks in higher contents of Ti and incompatible elements.
The Shirokaya beerbachite appears as 500 m-wide exposures in a long and wide field between the Krestovsky and Bora-Elga gabbro intrusions, flanked by marble melange exposures in the northwest and southeast. The beerbachite and marble melange fields are separated from the gabbro of the Birkhin complex by amphibolite in low amphibolite facies. In addition to the main, thick beerbachite body, there are a few other occurrences: 2–3 m to ~20 m fragments in marble melange; a 30 m × 8 m body within a small intrusion of the Birkhin gabbro, with buried gabbro–beerbachite contacts; and dismembered dikes in the Birkhin complex and in the marble melange field at the contact with the Ust’-Krestovsky gabbro.[[1]

Other Regions, Features and Areas containing this locality

References