30 research outputs found
A first insight into population structure and linkage disequilibrium in the US peanut minicore collection
Direct evidence of fluid mixing in the formation of stratabound Pb–Zn–Ba–F mineralisation in the Alston Block, North Pennine Orefield (England)
The North Pennine Orefield Alston Block has
produced approximately 4 Mt Pb, 0.3 Mt Zn, 2.1 Mt
fluorite, 1.5 Mt barite, 1 Mt witherite, plus a substantial
amount of iron ore and copper ore from predominantly
vein-hosted mineralisation in Carboniferous limestones.
However, a significant proportion of this production
(ca. 20%) came from stratabound deposits. Though much
is known about the vein mineralisation, the relationship
between the veins and the stratabound mineralisation is not
well-understood. New petrographic, isotopic and fluid
inclusion data derived from samples of stratabound mineralisation
allow us to present a unified model that addresses
the genesis of both the vein and stratabound styles of
mineralisation. The mineralisation can be considered in
terms of three episodes:
1. Dolomitisation and ankeritisation Limestones in the
vicinity of the stratabound mineralisation were pervasively
dolomitised/ankeritised, and developed vuggy porosity
in the presence of a high-salinity brine consistent with
fluids derived from adjacent mud and shale-filled basins.
2. Main stage fluorite–quartz–sulphide mineralisation
Metasomatism of limestone was accompanied by
brecciation, dissolution and hydrothermal karstification
with modification of the existing pore system. The
open space was filled with fluorite, galena, sphalerite,
quartz and barite, formed in response to mixing of lowsalinity
sodic groundwater with high-salinity calcic
brine with elevated metal contents (particularly Fe up to
7,000 ppm) relative to “normal” high total dissolved
solids sedimentary brines.
3. Late-stage barite mineralisation paragenetically
appears to represent either the waning stages or the
distal portions of the main hydrothermal circulation
system under cooler conditions