Mineralogy and origin of the distal volcanosedimentary deposit at the Haellefors silver mine, Bergslagen, central Sweden
In the Zn-Pb-Ag deposit of Hiillefors silver mine, four types of sulfide ores are recognized: l) stratabound ore associated with manganiferous iton ores, 2) arsenopyritebearing stratiform (stratabound ?) ore, 3) galena-rich fissures, 4) galena-arsenopyrite veins. Type 3 and 4 are thought to originate by remobilization from types I and 2, respectively. The antipathetic behavior of arsenopyrite with magnetite in the stratabound ores probably reflects environmental conditions during the deposition and early diagenesis. Metamorphic, hydrothermal remobilization led to the formation of many Ag, Pb and Sb minerals. Results of electron-microprobe analyses indicate that the principal sources of silver are argentian galena, freibergite and pyrargyrite. The silver content of galena (up to 0.17 wt.9o) has a linear relation with its antimony content. Tetrahedritegroup minerals contain ll.3 to 31.6 fi.qo Ag. An extremely silver-rich freibergite (48,2 wt.9o Ag) exceeds the previously reported maximum (42,5 wt.Vo).
COMPOSITIONAL TRENDS IN TETRAHEDRITE
Available mmpositional data for l27t samples of natural tetrahedrite and 295 of synthetic tetrahedrite were s1amingd. They show: compositional ranges of four to ten Cu, zero to six Ag, and a total of two (Fe, Zn, Hg) atoms, complete substitution (up to four atems) amongAs, Sb and Te, and a total of 13 atoms of S per formula unit. Data on contents of Pb, Bi and Cd in natural samples are insufficient to define their compositional ranges, and virtually no data exist on other substitutions, involving Co, Ni, Mn and Au. A generalized formula (Cu,Ag)6Cua@e,Zn,Cu,Hg, Cd)2(Sb,As,Bi,Te)a(S,Se)13 is proposed on the basis of these compositions. The cell rlimensisn is a linear function of chemical elements in the formula errcept inAg-rich tetrahedrite, where it increases with Ag content, up to four Ag atoms per formula unit, and then decreases. Ag and As have a low tolerance for each other in the structure, and plots of Fe versus Ag, Zn versus Ag, and Hg versus Cl suggest that incorporation of Ag'is controlled by several factors. For the purpose of explaining compositional variations in tetrahedrite, the simple Brillouin zone model of 6eading (Jotrnson & Jeanloz 1983) is superior to any ionic model.
Archaeological Survey of Dangoyama Kofun by 3DGPR
We presented a three-dimensional ground penetrating radar (3DGPR) system for the archeological investigation in a harsh site, where we have to deal with many trees and/or great topographic variations. This system consists of a commercial GPR system with a laser positioning system. With this system, we can move the GPR antenna freely, on which a positioning detector can record accurate position for each GPR data trace. We applied our 3DGPR system at Dangoyama Kofun, a burial mound, in Fukushima prefecture, Japan. A lot of trees and bushes covered the survey area and cannot be cut. We acquired six datasets in two days in this area. We successfully imaged the boundary between the original surface of the burial mound and the covering soil clearly at about 0.3 m depth around the mound. Furthermore, we found some strong reflections appeared at 0.8 m depth in the top area of the mound, which can be from the artificial parts of the burial mound. The results would greatly aid the following archaeological excavation. In addition, we compared the non-interpolated depth slice with interpolated depth slice at same position and demonstrated that the interpolation process on threedimensional GPR data may introduce some artifacts which might mislead our interpretation.