Removed samples from andesitic
rocks have 7ppm silver (Fig.
During this event, in the Middle Pleistocene, the Ajusco volcano was formed by the extrusion of several andesitic
This group is dominated by andesitic
to dacitic rocks with lesser quantities of basaltic to rhyolitic tuffs and flows and epiclastic sedimentary rocks.
Donoghue SL, Neall VE, Palmer AS (1995) Stratigraphy and chronology of late Quaternary andesitic
tephra deposits, Tongariro Volcanic Centre, New Zealand.
A similar but coarser, rough, blocky texture is seen on the surfaces of more andesitic
These include an interior andesiterhyolite assemblage of ash flow tuffs (31M-20M yr), a western assemblage of andesitic
lavas (20M-12M yr), and a bimodal basalt-rhyolite assemblage with associated sedimentary rocks.
The deposit is composed of vein systems located within a tertiary andesitic
The property geology is predominantly underlain Tertiary aged felsic volcaniclastic rocks which overlie a lower volcanic sequence of andesitic
flows and breccias, as well as intermediate composition volcano-sedimentary rocks.
Below the fault, the lithology changed to barren magnetite and hematite rich andesitic
The Cocos Plate is subducting beneath the Caribbean Plate along the Middle American Margin, building the Central Volcanic Range through magma ascent, and creating andesitic
massifs such as the one on which Turrialba volcano is located.
It continues: "The stone quarried at Harden was formed approximately 390 million years ago, when magma from deep underground was forced up into the surrounding andesitic
rocks, forming a thick blister-like intrusion of mica-porphyrite, which is now commonly called Harden red.
The lithology of the area consists of greenschists, mica schists, quartzites, hornblende schists, amphibolites, garnet-amphibolites, serpentinites and porphyritic hypabyssal rocks with andesitic
to dacitic composition (Figure 1).