山口縣玖珂郡桑根村付近の地質及び灰重石鉱床

This district is located at the eastern part of Yamaguchi-prefecture, and is geologically situated between the Sangun-Motoyama Metamorphic zone and the Ryoke outer zone, the latter of which is characterized by banded chert and slate. Characteristic feature of the Sangun-Motoyama metamorphic zone mainly composed of crystalline schists is represented by monoclinal structure, while the Ryoke outer zone is highly disturbed by folding, axial trend of which coincides with the general lineation (N80°W). The two geologic formations mentioned above are demarcated along a zone of breccia-bearing shear-slates including various kinds of brecctas of spindle-shape. Although these shear slates may often be regarded as the derivatives from a sort of conglomerate, it seems that they should be interpreted to have been formed through shearing action. Excepting the shear-slate, there are five kinds of rock types such as chert, slate, sandstone, limestone and porphyrite in the district.
There are many scheelite deposits which are, according to the mode of occurrance and paragenic relations of certain minerals, classified into the following two classes; one is the quartz-vein-type, the other the skarn-type, The presence of the deposits is generally confined in the surroundings of or within limestone wherein, however, only those of the skarn-type can be found; while also in the case of quartz-vein the amount of scheelite increases with approaching to limestone. Scheelite often paragenizes closely with quartz and adularia in the quartz-vein-type on one hand and with quartz, adularia, pyrrhotite and sphalerite in the skarn-type on the other. The mineral in question is believed to have been produced within the range from pneumatolitic to hydrothermal stage.
It seems that the appearance of the deposits has an intimate relationship with certain geologic structures since they are, as illustrated in the geological map, distributed merely along an anticlinal axis.