This process can result in not only the formation of broad alteration zones (i.e., greisenization and albitization
) [1,32], but also the variation of the fluid's composition and pH values (Figure 2) , sometimes playing a decisive role on the formation of hydrothermal ore deposits .
It is commonly associated with other types of alteration, such as albitization
, sepentinization etc., and with various types of mineralization, such as U or Mo mineralization.
On the whole, the temperatures calculated for the mineral assemblages span from 1250 to 1200[degrees]C and from 1130 to 1080[degrees]C, pheno- and microphenocrysts, respectively, under about 1kb H2O pressure and around 1000[degrees]C under atmospheric pressure; lower temperatures, for example, 900-700[degrees]C, suggest possible subsolidus exchange reactions (e.g., albitization
Wide range of anorthite contents in the plagioclase is due to albitization
. Apatite ilmenite magnetite and hematite occur as accessories and chlorite, calcite, stilbite, antigorite and clay are secondary.
However, it should be mentioned that volcanic Suursaari quartz porphyries have undergone intensive hydrothermal alteration (albitization
, epidotization, etc.) processes, which may have had some effect on the Ti content in quartz.
of microcline took place at around 300[degrees] to 400[degrees] C, followed by an acidic stage in which crystals of micas, fluorite and thick tabular albite crystallized from weakly enriched [CO.sub.2] solutions.
In the depocentre of the basin, a low-grade metamorphic event (hydrothermalism) took place, leading to some mineralogical changes in the original petrofacies, including silicification, chloritization and the albitization
This displacement is accompanied by hydrothermal alteration of granodiorite porphyries (chloritization and albitization
Four distinct alteration types are recognized: albitization
, potassic alteration, carbonatization, and silicification.
[Na.sup.+] can also be lost from the hydrothermal fluid due to Na-Ca replacement reactions in plagioclase feldspars, known as albitization