Environmental Engineering Reference
In-Depth Information
3). The Tm (ice) values of -40.3 to -40.6 ºC of the liquid-rich and the polyphase inclusions in
anhydrite from the deep reservoir strongly suggest that aqueous Ca comprises a significant
component, even though K or Fe may be contained as a minor component in these liquid-rich
and polyphase inclusions. The NaCl-CaCl 2 -H 2 O ternary model composition was therefore
determined by a graphical method (Vanko et al., 1988) using Tm (ice) and Tm (NaCl) for the
polyphase inclusion. The estimated composition is 11 wt.%NaCl and 24 wt.%CaCl 2 with total
salinity of 35 wt.% (table 6). Total salinities of the liquid-rich inclusions were estimated to
range from 22 to 29 wt.%NaCl+CaCl 2 eq. on the basis of the ice melting isotherms and the
liquid+ice+liquid+hydrohalite boundary (Oakes et al., 1990).
According to microthermometric and SEM-EDX studies of secondary polyphase
inclusions in igneous quartz in the Kakkonda granite (Sasaki et al., 1995), the inclusions
contain hypersaline fluids of 35 to 75 wt%NaCl eq., and daughter minerals consist of halite,
Fe-bearing chloride (containing minor amounts of Mn, K, Ca), sylvite (containing minor
amounts of Mn, Fe, Na), iron oxide (magnetite or hematite). Based on chemical analysis of
polyphase inclusion from a quartz vein in the Kakkonda granite using micro LA-ICP-MS,
major components are Na, K, Ca, Mn, Fe and Cl with minor amounts of B, Cu, Zn, Pb and
Ba, and trace elements of Li, Mg, Al, Rb and Sr (Sasaki et al., 1998). These hypersaline fluid
in polyphase inclusions was produced either by direct exsolution of the hypersaline fluid from
a magma (Roedder and Coombs, 1967; De Vivo and Frezzotti, 1994) formed the Kakkonda
granite or boiling of an aqueous solution (Takenouchi and Kennedy, 1965; Bowers and
Helgeson, 1983). Above polyphase inclusion data suggests that the hypersaline fluid was
released from the crystallizing magma itself.
The metal bearing hypersaline fluid was found from the deep exploration well WD-1a in
the Kakkonda granite (Kasai et al., 1998). Since the well did not encounter productive
fracture zone, fluid sample could not be directly obtained from the well. It was therefore
collected from 3708 to 3589 m in depths by reverse circulation using the drillpipe like a straw
to avoid contamination of the deep reservoir fluid with the shallow reservoir fluid within the
well. The hypersaline fluid consists of NaCl (15.0 wt%), FeCl 2 (9.7 wt%), KCl (7.0 wt%),
CaCl 2 (4.5 wt%) and MnCl 2 (2.5 wt%), ZnCl 2 (0.64 wt%) and PbCl 2 (0.14 wt%) with a total
salinity of 39.5 wt%. According to the estimation of the original hypersaline liquid prior to
dilution by circulation water using a tritium-salinity mixing model by Kasai et al.(1998), it
has a salinity of about 55 wt%NaCl eq., consisting of Na-Fe-K-Ca-Mn chloride, rich in Zn
and Pb but poor in Cu, Au and Ag. It thus has become clear that the hypersaline fluid in
polyphase inclusions is derived mainly from a residual magmatic fluid formed the Kakkonda
granite.
Figure 18 illustrates variation of total salinities with homogenization temperatures (Th) of
fluid inclusions (Muramatsu et al., 2000). The salinities of the liquid-rich inclusions with
lower saline fluids widely vary from 0.9 to 29 wt%NaCl+CaCl 2 eq. at Th values of 320 to 360
ºC in the deep reservoir. The lower saline fluids might have been produced by dilution of the
hypersaline fluid and boiling of the dilute fluids. The dilution should have been caused by
mixing with low saline fluids with temperatures of 320 to 360 ºC. As the liquid-rich
inclusions from the shallow reservoir contain low saline fluids ( 1.2 wt%NaCl eq.), the low
saline fluids are likely to be derived from a meteoric water conductively heated by the
Kakkonda granite intrusion.
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