Discriminant analysis for evaluating the use of lithogeochemistry along the Tetsusekiei Horizon as an exploration tool in search for Kuroko type ore deposits

Abstract

Tetsusekiei (literally, iron quartz) is in the form of thin, discontinuous beds that occur in the hanging wall of the Kuroko-type massive sulphide ores and at some distance beyond ore, along the uppermost part of the ore horizon tuff. The presence of tetsusekiei within a volcano-sedimentary sequence marks a horizon of fossil hydrothermal activity. Tetsusekiei shows elevated concentrations in trace elements of exhalative input relative to normal pelagic sediments and consists of two components; a clastic and a chemical component. Discriminant analysis applied to the following three groups: chemical component of tetsusekiei, clastic component of tetsusekiei and the upper part of the ore horizon tuff which is stratigraphically equivalent to tetsusekiei, has aided in providing the exploration geologist with a number of statistically significant major and trace elements that may be useful to exploration. The lateral distribution of the statistically significant major elements, expressed in the alteration index $$\operatorname{R} \% = \frac{{\left( {K_2 O + MgO} \right) \times 100}}{{K_2 O + Na_2 O + MgO + CaO}}$$ (Ishikawa et al. 1976) for the clastic component of tetsusekiei along the same stratigraphic horizon, shows an increase from about 50% to 90% approaching the Fukazawa mine from the northwest. The trace elements which are of exhalative origin show a relatively erratic distribution. In addition, the accommodation of barium, which is of exhalative origin, in the sericite constituent of the clastic component, combined with its higher concentration in the clastic relative to that in the chemical component, may indicate the presence of sulphide and/or barite ore lower in the stratigraphy.