The magmatic rocks are well developed and include Archean basicultrabasic rocks and granitoids, Proterozoic moyite, and Yanshanian quartz porphyry. The Yanshanian intermediate-acid intrusive rocks are closely associated with the mineralization, in which a large number of copper-molybdenum deposits had been produced (i.e., Changfagou, Tianhexing, and Ermi).
The faults associated with the metallogenic period exhibit NNW extensional shear properties, obviously controlling the orebodies and quartz porphyry. The faults associated with the postmetallogenic period destroyed the orebodies and porphyry to some extent and are NE compressive shear faults and NW, NNW extensional shear faults.
They range from micogranite (abundant) to aplite, pegmatite and quartz porphyry
, but the latter two are rare.
This new gold occurrence occurs at the sheared contact between a quartz porphyry
intrusion and mafic volcanic rocks.
Svecofennian orogenic rocks are covered with Mesoproterozoic sedimentary Hoglandium conglomerates and mafic (plagioclase porphyrite) and felsic (quartz porphyry) volcanic rocks of rapakivi formation (Koistinen et al.
Quartz porphyry samples were collected in the NW part of Suursaari Island (during the field work in 1987) at the Makiinpaallys Mountain outcrop.
Felsic rocks in the suite are mainly red to cream, fine- to medium-grained equigranular to porphyritic granite and tan and yellowish-green quartz porphyry. The granites are commonly highly fractured and limonite stained.
Well-rounded, red and green porphyry boulders, up to 0.5 m diameter, occur in a green quartz porphyry matrix.
The origin of the skarn is uncertain, but may have resulted from the intrusion of a quartz porphyry mass to the east, possibly during the Triassic.
It may have been mobilized from elsewhere in the skarn, or possibly introduced by magmatic fluids from the nearly quartz porphyry intrusion.
The Early Cretaceous subvolcanic rocks include quartz porphyry
and granite porphyry with a small amount of sulfides disseminated in these rocks observed in the drill cores, such as sphalerite and galena.
The outcrop of the largest quartz porphyry
body on Suursaari Island extends as a NNW-SSE belt for some I I km.