The geology of the Hitachi mining area is highly complicated by the original difference of rock facies, combined with various degrees of dynamic, contact and hydrothermal metamorphism. The deposits are developed along some sheared zones, especially located at some blind spots of stress. The ore might have been transported to such places by solutions, derived at much deeper zones of an orogenic belt, not. necessarily by magmatic intrusion, but perhaps by selective extraction of rock materials by superheated vapour there originated by dissociation of hydrous minerals. This supposed process is called “abyssal secretion”. Extraction of materials from strongly stressed country rocks and their deposition at local non-stressed points may be also possible-to some degrees. The term “lateral secretion” may be used also in sucha sense. Some deposits in this area, characteristic off high, temperature origin, may be those farther metamorphosed by later intrusion of granodiorite.

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On studying some shallow seated hydrothermal replacement clayey deposits, the alteration products of various volcanic or pyroclastic rocks in Japan, it was revealed by the present writer and some others that vertical and horizontal zoning of mineral assemblages exists in such a scheme as following:
Vertical zoning from upper to lower: silica→alunite→kaolin→pyrophyllite→diaspore.
Horizontal zoning from inner to outer: pyrophyllite-sericite montmorillonite, or sericite→chlorite or montmorillonite.
These deposits are confined within the earth′s crust to the depth of 1 km or less, indicating that they are of "vulkanisch" to "subvulkanisch" origin.
In the writer′s opinion, the zoning was caused by the action of acid mineralizing solutions of volcanic or subvolcanic origin on pre-existing rocks. The solutions became more acidic during the ascent as temperatures decreased from about 600°C. to 200°C. or 150°C.; they became more alkalic in lateral migration.
Among the components of the original rocks, most of the Si, Al and Ti seems to have been concentrated in some parts of the altered aureole, altkalies partly or selectively removed, while other components almost entirely removed. H₂O, Cl, B, F and S are the components which are obviously added from the mineralizing solutions.
Barth′s idea of the standard unite cell, oxygen=160, in calculation of the number of removed cations might be applied in some typical cases in Japan.

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The Kampaku Mine is situated about 20km north of Utsunomiya City, Tochigi Prefecture. The country rock of the deposits is biotite-liparite of late Tertiary age. The ore deposits consist of a vein like kaolin mass, two gold-bearing quartz veins, which are the foot wall of the kaolin mass, two dyxe-like silicified country rocks, which are the hanging wall of the kaolin mass, and kaolinized liparite which envelopes them. The deposits are banded, striking about N 60°W, and dipping 70°N.
Field observations indicate that kaolinization occurred along a fissure after the slicification of the country rock and the formation of the gold vein. Similar phenomena occurred also in the kaolinized liparite zone which has lower grade ore but greater volume.
The various examinations (microscope, electron-microscope, differential thermal analysis, chemical analysis, staining test and X-ray analysis) of the ores related to their localities revealed that kaolinization was caused by the upward moving hydrothermal solutions or hot spring containing sulfuric acid and that the qualities of the ores and crystallinity of kaolinite are better at the upper level and poorer at the lower. The kaolin minerals composing the ores are kaolimite containing some halloysite. The purely white kaolin has hardly any impurity except a small amount of very fine grained diaspore. The other kaolin masses commonly contain alunite, ferric minerals, quartz etc.

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