Rocks intrusive

Figure 1.73. Distribution of epithermal Au-Ag vein-type deposits, propylitic and advanced argillic alterations and intrusive rocks of diorite prophyry (Shikazono, 1985a).

The Seigoshi and Toi deposits occur in the andesitic pyroclastic rocks of the upper horizon of the Yugashima Group and basic intrusive rocks. Distributions of the wallrock alteration minerals from underground in the Seigoshi mine and on the surface near the... 

D and 8 0 data on fluid inclusions and minerals at main stage of epithermal Au-Ag mineralization clearly indicate that the dominant source of ore fluids is meteoric water. Meteoric water penetrates downwards and is heated by the country rocks and/or intrusive rocks. The heated water interacts with country rocks and/or intrusive rocks and extracts sulfur, Au, Ag and other soft cations (e.g., Hg, Tl) from these rocks. If hydrothermal solution boils, it becomes neutral or slightly alkaline, leading to the selective leaching of soft cations such as Au, Ag, Hg and Tl from country rocks. However, a contribution of sulfur gas and other components from magma cannot be ruled out. 

As already noted, most epithermal Au-Ag vein-type deposits are hosted by young (late Miocene-Pliocene) volcanic rocks and by sedimentary rocks, but dominant host and country rocks for base-metal vein-type deposits are submarine sedimentary and volcanic rocks. Submarine felsic tuff, tuff breccia, dacite lava, intrusive rocks and mudstone are dominant host and country rocks of Kuroko deposits. 

Obira deposit is located at south Kyushu. It occurs in Shimanto Group rocks composed of shale, and limestone, associated with middle Miocene granitic intrusive rocks. Polyascendant zoning and mineralization are observed in the Obira deposit. From early- to late-stage mineralizations are ... 

The other opinion is that the mineralization is related to bimodal volcanism. For example, in west Izu Peninsula, epithermal Au-Ag vein type deposits (e.g., Seigoshi) are associated with basic intrusive rocks and acidic volcanic rocks. 

Shinozuka et al. (1999) analyzed the host volcanic and intrusive rocks in the Minamidani mine district in the Maizuru tectonic Belt and found that these rocks formed in an island arc back-arc system near Laurasia during late Paleozoic. Probably the Yanahara deposits, one of the representative Hitachi subtype deposits, were formed in an island arc back-arc system as same as the Minamidani. Sato and Kase (1996) thought that the Hitachi-subtype deposits formed in back-arc rift or continental rift (Table 2.21). 

The geology of the study area comprises mainly limestones, shales, alluvial deposits and basic extrusive and intrusive rocks. 

Muscovite is the main term of the common dioctahedral micas, and it is found in acidic intrusive rocks (biotite and biotite-muscovite granites), although in subordinate quantities with respect to biotite. It is a common mineral in aplitic rocks and is peculiar to fluorine metasomatism in the contact zones between granites and slates ( greisenization ). 

The Miocene stratigraphy in the Baguio District has been intruded by a series of Pliocene rocks. The homblende-phyric Mafic Dike Complex intruded the central part of the Baguio District at 4.5 - 4 Ma (Waters et al. submitted). The complex is characterized by dense clusters of coarsely hornblende phenocrystic dikes with evidence for multiple injections. Several Pliocene to Pleistocene dioritic intrusive complexes are associated with porphyry copper-gold mineralization in the Baguio district. The Black Mountain Intrusive Complex includes the Black Mountain quartz diorite and the Mexico Diorite, as well as andesite dykes that have yielded ages of between 3.14 and 2.78 Ma (Waters et al. submitted Sweet etal. 2008). Other Pliocene intrusive rocks... 

A conserved element scatterplot of the hypogene lithogeochemical dataset (Fig. 2) illustrates that Zr/Ti02 ratios can be used to identify QB intrusive rocks. 

Two general areao in Colorado exhibit extensive alteration of coalo by igneouo intrusives. The first locality it near Somerset in the west central part of the state, and the second area is the Spanish Peaks region near Trinidad and Walsenburg. Drill core samples, outcrop samples, materials from active mines, and thin sections of the intrusive rocks were studied. The results show that mean maximum reflectance of the altered coal or natural coke increases as the distance from an intrusive body decreases. Carbon and ash values increase as the distance from intrusive decreases whereas volatile matter values decrease. Sulfur data are variable. Hydrogen values increase as the distance from an intrusive increases. Hydrogen and reflectance are considered the most sensitive and reliable indicators of degree of alteration. 

The feldspars crystallize from the magma in both extrusive and intrusive rocks they occur as contact minerals in veins, and they are developed in many sorts of tnelamorphic rocks, e g., albile schists. They may also he found as mechanical deposits in various sedimentary nicks. 

Intrusive A variety of igneous rock that cools and solidifies below the Earth s surface. Magmas solidify into intrusive rocks. 

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