Luminescence, color and fission track zoning in apatite crystals of the Panasqueira tin-tungsten deposit, Beira-Baixa, Portugal

Concentric growth zoning of apatite crystals from the hydrothermal tin-tungsten veins of Panasqueira, Portugal, is evidenced by variations in color, fission track density and luminescence intensity. The zoning was studied to determine its chemical controls and to evaluate its potential as a stratigraphic tool for paragenetic analysis and the correlation of veins. The apatites vary from green to colorless probably as a result of interaction between a green-producing chromaphore (most probably Fe2*) and REE decolorizing agents (possibly Nd3* and Ce3+). Fission track density is proportional to uranium concentration. The luminescence is yellow-orange and is characterized by four emission bands whose intensities were related to chemical concentrations by linear regression. The following activation models are proposed for three of these bands: (1) 349 nm emission (bandwidth {) nm). REE (Ce3+) activation, (2) 45 nm emission (bandwidth 40 nm). REE (Eu2+) activation, (3) 555 nm emission (bandwidth 100 nm). Mn2+ activation sensitized by Eu2* and Ce3*. The activation mechanism for the fourth band at 701 nm Oandwidth 50 nm) is unknown. The intensities of bands 1, 2 and 3 have a high degree of cross-correlation, and appear to be unrelated to band 4. Logging of emission intensity and fission track density across primary growth zones defines a highly detailed "stratigraphy" for €very crystal. Crystals from the same vug or the same mine pillar show strikingly similar "stratigraphies", but the maximum distance over which correlations can be demonstrated is only about ten meters.