836 REPORTS ON THE STATE OF SCIENCE. 
supply of Sweden have already been made. Professor G. Nordenstrom, 
the late Director of the Mining School in Stockholm, introduced for this 
purpose the conception of ore area, or ore section, 7.¢e., the horizontal 
section of the ore deposits expressed in square metres or square feet. 
Since most Archean ore deposits have a nearly vertical position, the 
horizontal section (=ore area) gives a comparative expression for the 
magnitude of the deposits. In 1893 he published a statement of the ore 
areas of the principal iron deposits of Sweden; in a completed and 
revised state he published it a second time in the year 1898, on the 
occasion of the meeting of the Iron and Steel Institute in Stockholm. 
The statement of Professor Nordenstrom shows in abridged form the 
following figures for the principal mining fields :— 
Ore Area in 
Norrbotten— Square Metres 
Kiirunavaara-Luossavaara . 4 A ‘ 430,000 
Gellivare r : 4 a p : ; ° 200,000 
Svappavaara . . . . : : : ; 38,000 
Central Sweden— 
Grangesberg . 5 : : - - 5 90,000 
Other mines in Central Sweden . ; 4 : 156,000 
Titanic Ores— 
Routivaara . 5 - 4 : : é : 300,000 
Taberg . . : : : : : : : 260,000 
1,474,000 m? 
The experience of later years has shown that the figures given by 
Professor Nordenstrém are in some cases much exaggerated. 
In order to convert the figures of ore area into tons of ore won by 
sinking the average level of the mine one metre, one has to take into 
consideration the weight of the ore and the percentage of ore in the rock 
mined, and by introducing also a measure for the depth, determined 
either by drilling or by magnetic survey, or simply by an estimation 
based on the experience from other mining enterprises in the same 
district, one may arrive at a figure for the probable ore supply of a mine, 
or of the whole district. 
In this way one gets an expression for the presumable ore quantity, 
or the ‘ ore expectant,’ as the American mining engineers express it.! 
Of course every such estimation leaves ample room for subjective 
discretion, and can at best only be considered as a rough approximation 
to the truth. The first estimation of this kind, comprising the whole 
country, was made in 1898, and is found in ‘ Vermlandska Bergs- 
mannaforen. Annaler’ for this year. The iron-ore supply of Central 
Sweden is estimated to be 110 M.T.,? and in Norrbotten at 520 M.T. 
Already in the previous year Mr. Hj. Lundbohm made an official survey 
of two of the greater ore deposits of Norrbotten, viz., Kiirunnavaara and 
Luogssavaara, and calculated the ore quantities obtainable above the level 
of Lake Luossajarvi to be in Kiirunnavaara 215 M.T., and in Luossavaara 
18 M.T. 
1 Ore expectant is ‘the prospective value of a mine beyond or below the last 
visible ore, based on the fullest possible data from the mine, and from the 
characteristics of the mining district.’—Philip Argall, The Engineering and Mining 
Journal of February 14, 1903. 
The ‘ore expectant’ deals rather with the future than with the present, and 
with the probable life of the property as a producing mine. 
2 Here and in the sequel M.T. means millions of metre-tons. 
