This causes the extensive stockwork brecciation. Further, boiling is an endothermic reaction requiring heat that is taken up from the magma as the escaping vapor expands, thus rapidly lowering the temperature of the magma chamber and producing the central porphyritic textured intrusive body. Additional evidence from Fluid Inclusions Studies of oxygen isotopes indicate that biotites from the potassic zone have values equivalent to those of magmatic waters. However, sericite of the phyllic zone is depleted in 18 O suggesting a meteoric water component. The same is true for argillic alteration.
Intrusion rises in the crust and begins crystallizing.
Convecting magmatic hydrothermal solutions produce potassic alteration within and immediately adjacent to the intrusive. Meteoric waters circulate convectively in the surrounding country rock to produce the propylitic alteration. The convection is driven by the heat from the intrusive. With cooling of the intrusive the meteoric system encroaches on the magmatic system developing the phyllic-argillic alteration zones. This leaves some interesting speculation.