Abstract
Epigenetic gold-quartz and scheelite-quartz lodes in Otago and other parts of the New Zealand geosyncline crosscut quartzofeldspathic and metavolcanic rocks of the pumpellyite-actinolite and greenschist facies. The lodes, which commonly strike north-west, are spatially associated with a 30 km wide belt of metavolcanic schists, with associated piemontite and sideritic schists, which parallels the axis of the geosyncline. A model is developed to account for the origin of the lode mineralization. A recent oxygen isotope study of the Glenorchy lodes suggested that the ore-bearing fluid was derived from rocks at depth over 150 degree C hotter than the lode formation temperature, and this is consistent with an origin by dehydration reactions at the greenschist to amphibolite transition. Hydraulic fracturing, induced by rapid uplift and unloading of the pile, allowed fluid migration to higher crustal levels where ore-deposition occurred. The spatial association of the lodes with the metavolcanic suite suggests that metals were derived by trace-leaching from the volcanic suite at the water source, or during migration, whilst tungsten may have been leached from associated manganiferous metasediments which commonly contain high anomolous concentrations of tungsten.
| Original language | English |
|---|---|
| Pages (from-to) | 180-196 |
| Number of pages | 17 |
| Journal | [No source information available] |
| Volume | 11 |
| Issue number | 2 |
| State | Published - 1976 |
ASJC Scopus subject areas
- General Engineering