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

Compositions of fluid inclusions containing halite and sylvite daughter minerals 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 attributed to halite precipitation from the fluid before trapping. Salt crystals observed in vein quartz crystals from mineralized zones in the Capitan Mountains, NM, USA, using an electron microprobe are evidence of halite precipitation causing the halite trend. The crystals (observed on both polished and broken sample surfaces) are often euhedral and enclosed in quartz with little suggestion of associated fluid cavities. Based on the textural evidence, these salt crystals are interpreted as solid inclusions that were trapped during the growth of quartz. Given halite-saturated fluids, trapping of heterogeneous (liquid+halite) fluid inclusions is possible, leading to the potential to overestimate the fluid inclusion salinities.