The Kosaka mine located in the northern part of Akita Prefecture has been well known for its typical kuroko mineralizations.
A number of unit ore bodies consisting of kuroko (black ore) and oko (yellow ore) are bedded in form and are underlain by the so-called white rhyolite that forms lava domes of various scales.
In recent years, many keiko (siliceous ore) bodies have been discovered within the white rhyolite. They are stock-work ores having cylindrical shapes as a whole, standing vertically, and grading into the overlying bedded ore bodies. There are two kinds of siliceous ore bodies: zinc-type and copper-type. The zinc-siliceous ore commonly grades into the copper one in lower horizons. The transition is well recognized by the variation in Cu/Pb/Zn or Cu/Pb + Zn ratios in the ores.
The volcanic activity of the white rhyolite is closely related to the kuroko mineralization, and the siliceous ore presumably represents the conduit of ore solutions.

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The deposits of the Higashiyama mine consist mainly of molybdenite-bearing quartz and clayey veins. Fluid inclusions are commonly found in quartz and calcite of the veins, and in quartz phenocrysts of host granitic rocks. Most of inclusions from the veins are composed of two phases consisting of liquid and gas. Three-phase inclusions consisting of liquid, gas and cube-shaped transparent solid are observed frequently in the phenocrysts of the granite porphyry.
Filling temperatures range from 262°C to 318°C for the host granitic rocks and from 156°C to 352°C for the molybdenite-bearing quartz veins. The filling temperatures increase westward from the Kawahira through Onobe to Higashiyama deposits, and higher temperatures are observed in deeper parts of the deposits.

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It is one of the important problems in explorating the Kuroko ore deposit to determine the prospecting target having an area from several to about ten times as wide as ore extent. In order to attack this problem, sulphur contents and magnetic susceptibilities of the drill cores from acid lavas widely underlying the ore deposits, have been measured. In the area surveyed is the Hanaoka-Shakanai deposit, one of the typical Kuroko deposits in Hokuroku district, Japan.
Reasons of selecting the acid lavas are as follows; (1) The stratiformed Kuroko deposit is of submarine volcanic sedimentary origin, and the followings are expected; Hanging wall rocks were altered only after the ore deposition, whereas foot wall rocks were altered through all stages of it. To catch the most widespread extent of the alteration, it is preferable to select the latter. (2) To check the variation of magnetic susceptibility of rocks, relating to the alteration, it is desirable that the primary distribution offerrimagnetic minerals in the rocks is homogeneous. It is probable that the rocks except lavas and intrusives have heterogeneous distribution of them. So that tuffs and mudstones are cut out. (3) When the prospecting method based on peculiar rocks found in an ore field has been established, the applicability of this method tends to be restricted within the ore field. Therefore, it is desirable to select the rocks associated commonly with this type of ore deposits. In many Kuroko fields, it is reported that acid lavas exist beneath the ore deposits.
By the measurements of sulphur content and magnetic susceptibility on 299 cores from 20 drill holes, the wide haloes of them have been recognized. In the limited extent surrounding the ore deposits, it is found that almost all of the drill cores from the acid lavas indicate high sulphur contents and low magnetic susceptibilities. Their bordering numbers to restrict the haloes are seemed to be S=0.3% and k=30×10^-6c.g.s./cm³, and the geometric mean values for each halo are S=0.74% and k=6×10^-6c.g.s./cm³. Outside of the haloes, the drill cores indicate low sulphur contents and high magnetic susceptibilities. Their geometric mean values are S=0.04% and k=105× 10^-6c.g.s./cm³, respectively. For cheapness and saving time for prospecting, it might be considered to use magnetic susceptibility only. But, in this case, there is possibility to catch the ghost halo of it. The best method to use the two indicators is magnetic susceptibility measurement of all cores as the first step, and the sulphur analyses of the cores indicating low magnetic susceptibilities as the second.
As the results of mineral separation tests by magnetism and specific gravity and of chemical analyses, it is considered that the formation of haloes of sulphur content and magnetic susceptibility is due to pyritization of magnetite included in the acid lavas.

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The Mamut mine, located in northwestern Sabah, about 65 kilometers east of Kota Kinabalu, is the first porphyry copper mine in Borneo.
The ore deposit had been discovered by the geochemical reconnaissance under the United Nations Labuku Valley Project. Commercial operation commenced in May, 1975 under the management of Overseas Mineral Resources Development. Sabah Bhd. Ore reserves are estimated at some 178 million metric tons of 0.476 percent copper.
The area is occupied by the Upper Cretaceous and Tertiary flysch type sediments and igneous rocks of the Northwest Borneo Geosyncline, extending over a distance of 800 kilometers in NE-SW direction. In the mineralized area, sedimentary rocks consist mainly of sandstone and siltstone of Palaeocene to Eocene in age, and are emplaced by serpentinized ultrabasic rocks. These rocks are intruded by adamellite porphyry and its small associates. These stocks may be apophyses of a large batholith underlying the area, represented by Mt. Kinabalu. Several data of potassium-argon age determinations indicated that the intrusives are very young, namely Upper Miocene to Lower Pliocene in age.
The size of main adamellite porphyry intrusive is approximately 800 meters long and 300 meters wide. This intrusive body is cut by later stage granodiorite porphyry dike.
The shape of ore zone or "ore-shell" is alike a upside down short jar and it has a maximan width of 450 meters and 800 meters in length with a depth of 200 meters. The extent of the ore-shell generally includes the boundary of the main porphyry intrusive, and within the ore-shell the copper grade is roughly constant slthough the host rocks are different such as adamellite porphyry, siltstone and even serpentinite.
The alteration zoning is somewhat dissimilar to LOWELL'S (1968) model although it is not yet elucidated in detail as his model. It is formed by quartz-biotite zone, tremolite-actinolite zone and hornblende (or fresh) zone from margin to centre of mineralized body. Secondary K-feldsper also occurs in this body. The ore-shell overlaps the quartz-biotite zone and "low grade cone" located in the hornblend zone.

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