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Vätskeinklusioner som ledtrådar till bildningsmiljön för Bölets manganmalm, Västergötland, södra Sverige

Borgenlöv, Camilla (1997) In Examensarbeten i geologi vid Lunds universitet
Department of Geology
Abstract
The hydrathermal manganese ores at Bölet, on the western shore of Lake Vättern, southern
Sweden, occupy fractures and fissures and form the matrix in brecciated zones in a granite.
Gangue minerals include barite, fluorite, quartz, calcite and some vanadinite and edingtonite
(Ba-zeolite). The ore consists mainly of manganite and secondary pyrolusite. Primary fluid
inclusions in quartz and fluorite were studied to determine the major chemical components,
salinity and temperature of the fluids that precipitated the ore. My results fit the eutectic
temperature (Te) of the system NaCl-CaCl2-H20 at -52°C. The temperature of formation (Th)
lies around 100°C and the total salinity is about 20 to 22 wt% (calculated from the final melting
... (More)
The hydrathermal manganese ores at Bölet, on the western shore of Lake Vättern, southern
Sweden, occupy fractures and fissures and form the matrix in brecciated zones in a granite.
Gangue minerals include barite, fluorite, quartz, calcite and some vanadinite and edingtonite
(Ba-zeolite). The ore consists mainly of manganite and secondary pyrolusite. Primary fluid
inclusions in quartz and fluorite were studied to determine the major chemical components,
salinity and temperature of the fluids that precipitated the ore. My results fit the eutectic
temperature (Te) of the system NaCl-CaCl2-H20 at -52°C. The temperature of formation (Th)
lies around 100°C and the total salinity is about 20 to 22 wt% (calculated from the final melting
temperature- Tm). These results agree with data from Fe-Mn-Ba and Pb-Zn ores in the Red
Sea rift. This together with the vicinity to Lake Vättern and the volcanism at Halle- and
Hunneberg indicates that the Bölet ore formed in a rift as well. The Permian magmatism of the
Halle- and Hunneberg may have initiated the hydrathermal circulation that precipitated the Bölet
ore. If so the age of the ore would be Permian like the Oslo rift magmatism. (Less)
Abstract
Popular summary: In my work I have studied the manganese ores at Bölet in Västergötland, southern Sweden. The ores at Bölet are of hydrothermal origin, which means that a hot fluid flushed through the bedrock and precipitated different salts and minerals. The purpose of the study was to determine the temperature of the precipitating fluids and to estimate their composition. To do so I examined microscopic cavities, so called fluid inclusions, filled with the fluid that once flushed through the Bölet bedrock. The inclusions studied were placed in the minerals quartz and fluorite, which are closely related to the ore minerals.

To find out the temperature of the precipitating fluids, which is approximately the same as the temperature of... (More)
Popular summary: In my work I have studied the manganese ores at Bölet in Västergötland, southern Sweden. The ores at Bölet are of hydrothermal origin, which means that a hot fluid flushed through the bedrock and precipitated different salts and minerals. The purpose of the study was to determine the temperature of the precipitating fluids and to estimate their composition. To do so I examined microscopic cavities, so called fluid inclusions, filled with the fluid that once flushed through the Bölet bedrock. The inclusions studied were placed in the minerals quartz and fluorite, which are closely related to the ore minerals.

To find out the temperature of the precipitating fluids, which is approximately the same as the temperature of formation for the hostminerals or the ore, you have to heat a small piece of the mineral, with inclusions in it, in a specially equiped microscope. When an inclusion is formed the cavity is filled to 100% with fluid, but when it cools of the volume of the fluid decreases. Since the volume of the cavity doesn´t decrease, a shinkage bubble is formed in the inclusion. When heating the inclusion, the shrinkage bubble disappears at the temperature of formation, or the temperature of homogenization (Th). The ores at Bölet were formed at temperatures between 80°C and 110°C.

To obtain the approximate composition of the fluid, frozen inclusions are heated and the temperature at which the very first melting occures gives a clue to the composition. This is extremely difficult to see. I got values between 0°C and 60°C with concentrations at 52°C, 57°C, 35°C. These values correspond with the first melting temperatures of the systems H2O NaCl CaCl2 ( 52°C), H2O NaCl CaCl2 MgCl2 ( 57°C) and H2O NaCl MgCl2 ( 35°C). 0°C would be pure water. Each system has a specific first melting temperature and it is called the eutectic temperarure (Te).

The salinity of the fluid can be calculated from the final melting temperature (Tm) which is when the last solid (ice) melts. This has been done in laboratories so I just compared my values with suitable tables and diagrams. The total salinities in my samples lay between zero and 22wt%. (Less)
Please use this url to cite or link to this publication:
author
Borgenlöv, Camilla
supervisor
organization
year
type
H1 - Master's Degree (One Year)
subject
keywords
geografi, geologi, vätskeinklusion, Bölet, manganmalm, Västergötland, Sverige
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
86
language
Swedish
id
2365469
date added to LUP
2012-10-29 13:41:17
date last changed
2012-10-29 13:41:17
@misc{2365469,
  abstract     = {Popular summary: In my work I have studied the manganese ores at Bölet in Västergötland, southern Sweden. The ores at Bölet are of hydrothermal origin, which means that a hot fluid flushed through the bedrock and precipitated different salts and minerals. The purpose of the study was to determine the temperature of the precipitating fluids and to estimate their composition. To do so I examined microscopic cavities, so called fluid inclusions, filled with the fluid that once flushed through the Bölet bedrock. The inclusions studied were placed in the minerals quartz and fluorite, which are closely related to the ore minerals.

To find out the temperature of the precipitating fluids, which is approximately the same as the temperature of formation for the hostminerals or the ore, you have to heat a small piece of the mineral, with inclusions in it, in a specially equiped microscope. When an inclusion is formed the cavity is filled to 100% with fluid, but when it cools of the volume of the fluid decreases. Since the volume of the cavity doesn´t decrease, a shinkage bubble is formed in the inclusion. When heating the inclusion, the shrinkage bubble disappears at the temperature of formation, or the temperature of homogenization (Th). The ores at Bölet were formed at temperatures between 80°C and 110°C.

To obtain the approximate composition of the fluid, frozen inclusions are heated and the temperature at which the very first melting occures gives a clue to the composition. This is extremely difficult to see. I got values between 0°C and 60°C with concentrations at 52°C, 57°C, 35°C. These values correspond with the first melting temperatures of the systems H2O NaCl CaCl2 ( 52°C), H2O NaCl CaCl2 MgCl2 ( 57°C) and H2O NaCl MgCl2 ( 35°C). 0°C would be pure water. Each system has a specific first melting temperature and it is called the eutectic temperarure (Te). 

The salinity of the fluid can be calculated from the final melting temperature (Tm) which is when the last solid (ice) melts. This has been done in laboratories so I just compared my values with suitable tables and diagrams. The total salinities in my samples lay between zero and 22wt%.},
  author       = {Borgenlöv, Camilla},
  keyword      = {geografi,geologi,vätskeinklusion,Bölet,manganmalm,Västergötland,Sverige},
  language     = {swe},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {Vätskeinklusioner som ledtrådar till bildningsmiljön för Bölets manganmalm, Västergötland, södra Sverige},
  year         = {1997},
}