In the Nakatatsu mine of pyrometasomatic lead and zinc deposits, the recent systematic exploration activities in the Kurotodo area have resulted in the discovery of new minable orebodies with further ore potentials to be explored. The Kurotodo deposits are located in the westernmost part of the Nakatatsu mine area. It is revealed that in the Kurotodo area the Fujikuradani limestone formation of possible hosts of ore deposits is emplaced in a wider area at the depth.
In the northern, central and southern areas of the Fujikuradani formation are found new mineralized zones associated with skarn minerals which consists mainly of garnet with some clinopyroxene, wollastonite, etc.
In the mineralized zones in the northern area are found promissing orebodies, several of which in the east are now under development.
In the northern area the skarn minerals consist largely of garnet in the east mineralized zone, and are relatively rich in clinopyroxene in the west mineralized zone.
In the central and southern area the mineralized zones consist predominantly of garnetiferous Shiroji, composite of quartz calcite and ore minerals, and wollastonite. The Kurotodo deposits comprise lead and zinc orebodies of irregular masses in shape in the same manner as the main deposits of Nakatatsu mine. On the other hand in the central area are partly found vein-like orebodies in shape.
The study of Pb: Zn: Cu ratio [π-Pb=Pb(%)×10×100/(Zn(%)×1+Pb(%)×10+Cu(%)×100)] has revealed that the Kurotodo deposits are remarkably higher in π-Pb than the main Nakatatsu deposits and that the areas high in π-Zn or π-Cu are confined only to small areas in the east mineralized zone of the northern area.
It has been also revealed that the Kurotodo deposits are of low value in Ag/Pb ratio with the exception of a part of the north mineralized zone.
In these respects, the Kurotodo deposits are different from the main deposits in the Nakatatsu mine. The mineralization in the area is controlled by faults such as the Ohno fault and the Uwaban fault with a east-west trend and by fissure systems with a north-south and northeast-southwest trend.
The igneous rock related to the mineralization in the area is presumed to be quartz porphyry which is located northeast of the Senno deposits and is considered to be the related igneous rock of the main ore deposits in the Nakatatsu mine.

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The kuroko deposits of Kosaka mine consist of several types of ores such as black ore (BO), semi-black ore (SBO), yellow ore (YO), and siliceous ore (SO). The SO may be subdivided into black-SO (BSO) and yellow-SO (YSO) on the basis of ore mineralogy and further into massive-SO and stockwork-SO from the structural and textural characteristics. Present study on the stockwork-SO has provided the following information:
(1) Orebodies of stockwork-SO in general display a sort of cylindrical form with average dimension of about 40m×20m×70m.
(2) In terms of ore types included, they are classified into two groups, i.e., Uchinotai type characterized by the combination of YSO-YO-SBO-BO and Uwamuki type of YSO-BSO-BO. The Uchinotai type are developed dominantly in the central portion of the deposits, while the Uwamuki type are restricted in occurrence to their marginal portion.
(3) Distinct chemical zoning is recognized in some orebodies named as 4D-W (Uwamuki type), P-O (Uchinotai type) and 2D-W (Uwamuki type), i.e., Cu→Cu+Zn→Cu+Zn+Pb in the former two and Cu→Cu+Zn→Zn+Pb in the latter, in vertically ascending order. The zoning patterns in the orebodies 4D-W and 2D-W are obviously asymmetrical on the vertical section.
(4) Paying attention to total composition, the P-O orebody is slightly enriched in Cu and depleted in Zn+Pb as compared with the 4D-W orebody. In view of the distribution of Cu, Pb, Zn and Ag among different ore types, the ore type BSO in the 4D-W orebody is assumed to be chemically equivalent to the sum of YO, SBO and a part of BO in the P-O orebody.

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The tungsten-copper-tin deposit of the Takatori mine is of plutonic vein type and developed in alternating beds of sandstone and shale which constitute Yamizo Group of Triassic age. Detailed examination on the mode of occurrence of the deposit both in the underground and in the field has provided some important informations and suggestions for future exploration. Our observations and conclusions in this study may be sum-marized as follows:
(1) Vein fractures in the deposit are classified into two groups, i.e., "Tatehi" group and "Yokohi" group. Fractures of the former in general trend NWW-SEE and steeply dip southward, while those of the latter are almost horizontal but in general gently dip northward. The two groups of fractures constitute a set of conjugate shears under the same stress field, principal stress axes of which being as follows; maximum compressional stress axis (σ₁): S25°W30°, intermediate compressional stress axis (σ₂): trending NWW-SEE and nearly horizontal, and minimum compressional stress axis (σ₃): N30°E60° with angle of shear planes (2θ) of 80°.
(2) Three mineralization stages are identified, i.e., wolframite-quartz stage, sulfide-quartz and cassiterite-quartz stage, and barren quartz stage with only pyrite, in chronological order.
(3) At Nanabanhi Vein, the champion vein of the deposit, a vertical metal zoning is clearly observed, i.e., wolframite-rich zone, chalcopyrite-rich zone and cassiterite-rich zone in ascending order.
(4) The localization of ore shoot appears to be structurally controled by some faults named as No.7 fault, No. 15 fault and W28 fault at-7 level, among which No.15 fault, being located in the central part of the deposit, is assumed to have acted as a channel feeder of ore fluid. All the faults were formed prior to the mineralizations and were probably in active during a certain period after the mineralizations as well.
(5) It is suggested that the vein fracture systems were related in origin to the intrusion of a granitic magma. Namely, the uplifting of the southern geologic block with northwestward tilting at the stress field given by the granitic intrusion is considered to have been responsible for the reverse S-shaped regional structure of the area to have resulted the vein fracture systems observed.

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In order to disclose the formation processes of veins of the Motoyama deposit, Toyoha mine, an attempt has been made to examine collectively their geologic and tectonic setting, structural controls and mode of distribution of ore metals. Some of our conclusions are summarized as follows:
(1) Fissure systems responsible for the mineralizations are due primarily to the formation of a caldera-like tectonic depression with 5km×4km in horizontal dimension, which was probably followed by the emplacement of the dacite lava dome extruded at a certain period of late Koyanagizawa stage.
(2) The mineralizations can be divided chronologically into two groups, i.e., early stage mineralizations and later stage mineralizations. Between the two groups of mineralizations is a striking contrast in mode of distribution of ore elements, especially as to Pb/Zn ratio and total sulfides content.
(3) Fissures of Tajima and Izumo veins are suggested to have played principal roles as source feeders of ore fluids responsible for the two groups of mineralizations in the Motoyama deposit.

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Geostatistical method was applied to solve the question, if we had done enough drilling to estimate considerably accurate ore reserve figures at the final exploration stage of Kutcho deposit, which is a bedded massive sulfide deposit located in northern B. C., Canada. The accuracy which we required would allow the estimation error less than around 10% in regarding the metal contents in the proposed annual mining area. At the end of 1980, two years final exploratory drilling program was planned after the geostatistical evaluation of the existing drilling results, expecially regarding to design the drilling interval and pattern. On the half way of that program, the results adding new drillings were re-evaluated geostatistically, then concluded we already reached the proposed accurate level and there was no neccessity to continue the rest of the drilling program. After the drilling, ore reserve culculation has been done using Kriging method, and using Inverse Square Distance method for comparison. Then concluded, Kriging method is apparently recognized better than Inverse Square Distance method. And geostatistical evaluation is recognized to be useful for designing the drilling interval and pattern in our case.
Symposia on applying geostatistics to evaluate ore deposits have been frequently held in Western countries, while rarely done in Japan. We hope this report will have a chance to enhance geostatistics more popular in our country.

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