Eleventh International Geological Congress. z< 



seen, without any immediate limestone association. The granite 

 eruptives may also in some instances have been active mineralizing 

 agents. Granulite or leptite is abundant, cut by skarn zones, which 

 contain the ores. 



The history of the Sala lead and silver mine extends over four 

 centuries. The ore deposits seem to have been discovered early in 

 the lGth century, being mentioned in a document dated September 

 1, 1510. Its palmy days were in the early half of the lGth century. 

 when it furnished an important part of the public revenue. By 

 1571 mining operations were difficult on account of water. Kings 

 Carl IX. and Gustavus Adolphus both tried their hands at it; but 

 for fifty years only little progress was made. The grade of the ore 

 declined with greater depth, and renewed exploration in the upper 

 levels discovered more ore once in the latter part of the 17th cen- 

 tury and again a hundred years later. It is stated that the mint- 

 was worked at a loss during the whole of the 19th century. At 

 present an effort is being made to utilize the zinc ores that were 

 left in the mine by former operators. 



The total production of silver of the Sala mine is estimated at 

 about 400 tons, of which about one-half was produced in the 16th 

 century. Sjogren states that from an economic point of view the 

 mine was run at a loss for three centuries. It was kept going only 

 by means of special privileges from the Crown. 



We find here again the crystalline schists or basal complex of 

 halleflinta and limestone, cut by granite and porphyrite intrusions 

 and by later diabase dikes. The carbonate rocks are most closely 

 connected with the ores. The galena is found chiefly in the lime- 

 stones and only to a very subordinate extent in the halleflinta. 

 Copper ores also occur in the limestone; while small iron mines in 

 the district are connected with the halleflinta. 



This latter rock here presents an extremely varied formation 

 whose only common character is the felsitic texture of the ground- 

 mass. It is dark, or light gray or brownish, and is sometimes 

 striped or banded. A few varieties have a purely granitic or quartz- 

 porphyric constitution; in general, however, the percentages of al- 

 kali are lower than in the quartz and felsitic porphyrites, and the 

 constitution corresponds rather to that of the dacites and quartz- 

 porphyries, with which rocks the halleflinta also shows points of 

 agreement in the quantity of Fe — Mg silicates. On the whole, the 

 rock in its composition stands closest to the intermediate eruptives. 

 The percentage of lime, which preponderates over that of Mg. and 

 the often considerable percentage of Xa, which often outweighs 

 the K, forbids the interpretation of it as a metamorphosed sedi- 

 mentary rock. It grades into the dolomite limestone both by an 

 increased percentage of the calcareous material and by close inn t- 

 banding. 



The fact was noted at an early date that the ores declined in 

 richness toward the deep. This phenomenon, which is not peculiar 

 to Sweden, is commonly ascribed to secondary enrichment from the 

 surface downward; but Prof. Sjogren, to whom we are indebted for 

 a description of many of these mines, and who went with us as 

 guide, philosopher and friend, does not accept that theory h« 



