A wide geothermal field, consisting of six basins, around Mt. Waita in central Kyushu contains a large number of steaming grounds and hotsprings. Two geothermal power plants are also located in this area. Since FY 1978, a national project was started to survey deep geothermal resources in this field. As a part of the project, 81 bore holes (80m-depth) were drilled. The mean heat conductivity of the mostly andesitic cores from these bore holes is 3.90×10^-3 cal sec^-1 cm^-1 deg^-1. The distributions of subsurface temperature and heat flow observed in these bore holes indicate five anomalous areas with high heat flow. Formulae providing the standard temperature at 20m-, 50m- and 80m-depth with respect to the height above the mean sea level were developed using the temperature data obtained from 39 bore holes located in the normal-heat-flow areas. Geothermal gradient in lowland areas is larger than in the highlands around Mt. Waita. In order to discuss the geothermal condition of the field, the heat discharges from the six basins are estimated. Their total is about 143, 500 kcal sec^-1, of which 5, 030 kcal sec^-1 by conduction, 9, 690 kcal sec^-1 by hotsprings, 27, 550 kcal sec^-1 by fumaroles and the remaining 101, 200 kcal sec^-1 by steaming wells including the two power plants. A half of the total water discharge (1, 980 thr^-1) is attributed to hotsprings. Comparing the convective heat discharge from the field, except Kuju-Iwoyama and the two power plants, with the two nearby geothermal fields, Beppu and Yufuin, the field has 22% of the total discharge of Beppu and is about 1.7 times larger than Yufuin.

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On early 2016, the BCOM (Bloomberg Commodity Index) seems to pass over the bottom where the value was nealy equal to the one recored on middle 2008. Many remarkable results have been reported, however, in the explolation and production fields of minerals and energy resources as follows: 1) the indicated resources became almost two times in the Waterberg PGM project, South Africa, 2) the production of copper cothod started at the Antucoya mine, Chile, 3) the field development plan was approved for the Culzean high pressure and high temperature gas condensate field in UK North Sea, 4) it commenced oil production from Lianzi field situated in a unitized offshore zone straddling Angola and the Republic of Congo, 5) the North West Shelf Project has made a final investment decision on the Greater Western Flank Phase 2 gas fields development project off the north-west coast of Australia, 6) Japanese companies joined exploration projects opareting in offshore oil and gas fields, NE Brazil, and 7) the official opening was held at the Maules Creek coal mine, Australia. A long term LNG sale and purchase has been signed using U.S. Henry Hub natural gas-linked prices, and other following agreements adopted the system. In the geothermal development, offering a type of insurance has been begun in order to ease the concern of hot springs operators about the impact of new geothermal power stations.

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White colored alteration halos are widely distributed at the surface of studied area. These alteration halos are divided into four types based on their mineral paragenesis. Characteristic minerals are pyrophyllite and dickite (type I), alunite and kaolinite (type II), cristobalite and alunite (type III) and quartz and K-feldspar (type IV). In addition, green colored alteration zone characterized by chlorite and zeolites (type V) are widely distributed under the ground of geothermal areas. Clay minerals can be found X-ray diffraction analysis of samples separated by dispersion procedure from rocks which are generally considered as fresh rock. These data are very useful for the analysis of water flow of regional scale. Distribution patterns of montmorillonite indicate the path of shallow hot water flow and those of halloysite coincide with deep faults which were identified from the analysis of radar images. The distribution of thermal manifestations and alteration halos is fairly controlled by the deep faults which cut the basement rock but has less relations to E-W directional active faults and linearments which are intensely and clearly identified from the analysis of aerial photograph. Based on the types and distribution patterns of alteration minerals, ages of volcanic rocks and history, present model of hydrothermal systems of the area are inferred. An important point of the formation of hydrothermal systems in this area is the presence of Tertiary basin. Within the basin, fine-grained sedi-ments and formations which took place regional scale hydrothermal alteration prevent the intrusion of large amount of cold waters to deep part and preserve the heat source. After that, many geothermal activities have been occurred and formed many kinds of alteration halos in accordance with their physico-chemical conditions of the areas.

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