Abstract
Wakamatsu chromite mine has a largest chromitite-pod called "nanago-ore body (7th ore body)" which is 40×210×25m (2.1×105m3) in size in Japan. The other chromitite-pods which are intermediate size (4.5×104-1.2×103m3) are also distributed in Wakamatsu mine. We have clarified that the relationships between chromian spinel in chemistry and size of chromitite for exploration for podiform chromitite. Major results of this work are as follows.
(1) Nanago ore body is larger than the other chromitite bodies by one order of magnitude.
(2) Chromitite bodies are divided into two groups by Cr# of chromian spinel from chromitite that are high-Cr# group (Cr#:0.52-0.57, nanago and 10th ore bodies) and low-Cr# group (Cr#:0.41-0.48, 51st, 52nd, 53rd, 54th, 55th, and 56th ore bodies).
(3) Cr# of chromian spinel in dunite envelops varies from 0.45 to 0.62 in "nanago and 10th ore bodies group" and 0.48 to 0.57 in "the other chromitite ore bodies group."
(4) Chromian spinels from dunite envelops in both Nanago and the other chrmitite bodies are plotted in relatively high-Cr# and low-V2O3 field on Cr#-V2O3 diagram of Matsumoto and Arai (1997).
The results of above characteristics clearly show that spinel precipitation and concentration are more intense at nanago ore body than at the other chromitite bodies of the Wakamatsu mine. And that to explore the podiform chromitite, Cr#-V2O3 relation is useful petrological exploration tool not only for relatively large chromitite but also for intermediate one.
