Removing Inclusions From Crystals by Gradient Techniques

Abstract

Gradient techniques for moving inclu-sions out .of crystals are not only ripe for^ application, but also 'present opportunities for, discovery . . and investi-5Hs0, N a A O r . 10H~0, Ba(NO&, KIOa, KI, KBrG, K d O a , potwium biphthalate, urea, naphthalene, benzoic acid, oxalic acid, thiourea, and hexamethylenetetramine reagents. Gas bubbles were present in Na&Oa. 5H10, NarB4Oi. 10H10, Ba(NOa)t, (NH&),Ce-(NOa)a, KIOa, KI, e r O a , KClOa, "anhydrous"NalCO,, benzoic acid, and hexamethylenetetramine reagents. The liquid inclusions in NarSzOa. 5HsO also contained many minute rod-shaped crystals.As will be shown later, isothermal heating to the vicinity of the boiling point of an included solvent is insufficiwt to remove it from the crystal. Indeed, hiating to decrepitation d q not even guarantee elimination of included solvent. The alternative discussed here is the use of gradient techniques to move the inclusions through h d out of the crystal in a more or less gentle fashion.For the pu-of discussion we use the concrete ex-

Brine flow in heated geologic salt.

“…Wilcox (1968) indicated heating crystals to the decrepitation point associated with large brine inclusions does not always rupture smaller inclusions in the same salt. Roedder and Belkin (1980) performed brine migration studies on ERDA-9 core where fluid inclusions were found near crystal boundaries.…”

“…When brine inclusions reach the intergranular porosity between crystals, they tend to stay there, without migrating into the adjacent crystal (Olander, 1982). When inclusions have > 10% gas content (i.e., biphase) they will often migrate faster than brine-only inclusions, but they will move down a thermal gradient, away from the heat source (Wilcox, 1968(Wilcox, , 1969Anthony and Cline, 1972). As evidenced by geologic brine inclusion stability under geothermal gradients, brine inclusion movement is apparently subject to threshold temperature gradients (Gnirk et al, 1981;Krause and Brodsky, 1987).…”

“…Brine inclusion decrepitation is failure due to the stress generated by the included phase's vapor pressure, and the differential thermal expansion of salt crystal and brine inclusion (Wilcox, 1968). Upon decrepitation, intragranular brine escapes the local crystal structure, becoming intergranular brine (Figure 2.1).…”

“…Decrepitation temperature can vary by confining pressure and inclusions size. Inclusions have been shown to grow in size and gas content upon heating to temperatures below decrepitation (Wilcox, 1968;Roedder and Bassett, 1981).…”

“…The decrepitation point depends on the composition of the evaporite, and has been observed to vary between different sized inclusions (Wilcox, 1968). Appendix A discusses laboratory brine characterization tests, which included decrepitation observations.…”