Solid inclusions of halite in quartz: evidence for the halite trend

Compositions of fluid inclusions containing halite and sylvite daughter min erals can define a linear trend of decreasing salinity when plotted in the NaCl-KCl-H2O ternary system. This is termed the Halite Trend, and is attrib uted to,halite precipitation from the fluid before trapping. Salt crystals observed in vein quartz crystals from mineralized zones in the Capitan Moun tains, NM, USA, using an electron microprobe are evidence of halite precipi tation causing the halite trend. The crystals (observed on both polished an d broken sample surfaces) are often euhedral and enclosed in quartz with Li ttle suggestion of associated fluid cavities. Based on the textural evidenc e, these salt crystals are interpreted as solid inclusions that were trappe d during the growth of quartz. Given halite-saturated fluids, trapping of h eterogeneous (liquid + halite) fluid inclusions is possible, leading to the potential to overestimate the fluid inclusion salinities. (C) 2001 Elsevie r Science B.V. All rights reserved.