leptothermal

CONT: On sépare quelquefois un type «leptothermal», qui correspond à la partie supérieure du mésothermal, sans posséder franchement les caractéristiques épithermales. Les textures rubanées et drusiques y sont plus développées que dans le mésothermal; le grain plus irrégulier.

CONT: ... epigenetic-hydrothermal deposits are classified according to their depth and temperature of formation - hypothermal deposits being deep-seated high temperature deposits; mesothermal deposits those formed at low temperatures and medium depths, and, thirdly, epithermal, near-surface deposits. Later terms include leptothermal to cover deposits gradational from mesothermal to epithermal, and telethermal for very low-temperature deposits formed at great distances from the source of the hydrothermal solutions which gave rise to them.
OBS: leptothermal ... Mineral grain size averages smaller and more variable than in mesothermal ores. There is an increased development of vugs toward the shallower limit of the zone. Rock alteration varies from sericitic to propylitic. Vertical depth range is estimated from 10,000 to 15,000 feet.