On the occurrence of the No. 11 ore deposit in the Shakanai mine

Abstract

In the Shakanai mine, ore deposits that have been discovered to date enumerate 11 in number. The mine runs at 26, 000 tons of crude ore production per month. Of the ore deposits mentioned above, No. 11 ore deposit, discovered in the latest, has been exploited since 1974 and is now conducing to the 1/4 production of total crude ore produced in the mine. The No. 11 ore deposit is divided into South ore deposit and North ore deposit, and is composed of high grade black ore and disseminated ore. The south ore deposit is considered to be main ore deposit of the two and mode of its occurrence has been revealed as follows.
1) Ore deposit is composed of black ore and siliceous disseminated ore and lie in two definite stratigraphic horizons.
2) Ore deposit lies only in B bed of Shakanai upper member which extends to NNW-SSE direction elliptically in the area of 400m×250m.
3) B bed consists of dacitic tuffs, breccia bed, basaltic tuffs and mudstone. The breccia bed is most important host rock, and basaltic tuff and mudstone constitute the hanging-wall having tendency to increase the thickness of bed on the center portion of ore deposits and to decrease it on the outside.
4) Observing ore shoot in each unit ore body, it is inferred that deposition of ore was performed along the small scale troughs on the foot-wall.
In addition to these occurrences, such rare minerals as stromeyerite, renierite and unidentified mineral of Cu-Pb-Ag-S system were observed in small amount by EPMA.