1988 Volume 38 Issue 211 Pages 457-467
Tungsten deposits of the Yaguki mine occur as layered, lenticular, massive and amoebic forms in intensely altered clinopyroxene and garnet skarns along the contact with the limestone at hanging wall. The skarns were hydrothermally altered to aggregates of actinolite, epidote, quartz, prehnite, chlorite, sericite, calcite, scheelite. Scheelite occurs as disseminated grains, veinlets and networks in the alteration zone. Under the microscope, it is euhedral to subhedral, and is 0.15 to 2.0 mm in size. This mineral is intimately associated with epidote, quartz and, sometimes, prehnite. Scheelite also occurs with chlorite, sericite and calcite which were crystallized at later stage than that of scheelite.
Ore minerals such as magnetite, pyrrhotite, chalcopyrite, pyrite, sphalerite, bismuthinite and native bismuth appear occasionally with scheelite in the altered skarn. Veinlets of quartz with scheelite sometimes penetrate into magnetite, meanwhile scheelite is surrounded by the sulfide minerals, and cut by veinlets of them.
Temperature and sulfur fugacity of sulfide mineralization obtained from data of ore mineral assemblages and iron contents of sphalerite are 240°to 290°C and 10-14 to 10-12 atm., respectively.
Molybdenum content of scheelite is less than 10.1mol% CaMoO4, commonly less than 3.0mol% CaMoO4. Zontal structure is usually found in scheelite crystals in term of Mo contents. The central part of the crystal has relatively higher Mo contents than those of outer portion. Crystals are often rimmed with pure scheelite, and sometimes cut by its veinlet.
