---I can't say for sure from the limited context, but I would tend to interpret "copper activity" in your sentence as "銅活性" which is focused (集中されている）on deposits near the XX area.

----That is, there is is copper activity present in that particular area. (As opposed to this being about "business activities regarding copper.")

Here are some sample websites about finding copper activities in various soils:
http://www.ncbi.nlm.nih.gov/pubmed/16781806
Abstract
Copper partitioning was studied in seven calcareous soils at moisture content corresponding to 1.2 times the field moisture content (soil water potential 7.84 J kg(-1)). Copper retention was accompanied by the release in soil solution of Ca(2+), Mg(2+), Na(+), and H(+), and the total amount of these cations released was 0.8 to 1.09 times the amount of Cu sorbed (mol(c):mol(c)). The relationships between Cu activity and pH, and the balance of cations in soils correspond with the surface precipitation of CuCO(3) as the main mechanism of Cu retention. The values of ion activity product of surface precipitate were close for all studied soils with the average log(IAP(CuCO(3)))=-15.51. The relationship between copper activity in soil solutions and soil properties is well fit by a regression relating pCu (-log copper ion activity) with soil pH, total Cu, and carbonate content.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V...
Copper activity in soil solutions of calcareous soils

http://www.springerlink.com/content/f27371442230704n/
Effect of copper activity on carbon and nitrogen mineralization in field-aged copper-enriched soils




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Note added at 22 hrs (2010-09-09 13:29:36 GMT)
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----- One more thing that makes me think it is "銅活性"....

----- "Copper activity" alone would be incomplete in an English document to express the term 銅における（探鉱企業の）事業活動.

----- The most common phrase for 銅における（探鉱企業の）事業活動 would be "copper mining activities" (which gets a lot of hits.)