THE HEEMSKIRK MASSIF , 165 



15— THE HEEMSKIRK MASSIF— ITS STRUCTURE AND RELATION- 

 SHIPS. 



By L. KEITH WARD. B.A., B.E. 



CONTENTS. 

 I. — Introduction. 



II. — The Proximate Source of Igneous Rocks and Metallic Ores. 

 III. — ^The Structure of the Heemskirk Massif — 

 {a) The Visible Contours 

 {h) The Invisible Contours 



i. In a horizontal Direction 

 ii. In a vertical direction. 

 IV. — The Relation of the Heemskirk Massif to Neighbouring Massifs 

 of Similar Composition. 

 V. — Conclusion. 



[Pl.\TES .XIII. AXD XIV.] 



I. — Introduction. 

 Most students of that branch of geological enquiry which is con- 

 cerned with ore deposits have within recent years come to believe 

 that a large number of ore deposits are genetically related to masses 

 of igneous rock material which are to different degrees exposed in 

 the immediate vicinity of the ore bodies. 



With the progress of systematic mapping it has become 

 apparent that ore deposits are distributed unevenly among the 

 rocks of different ages, and that thus the periods of ore deposition 

 may be determined. For example, the majority of the ore 

 deposits in Tasmania are distributed through rocks of which the 

 age ranges between the pre-Cambrian and the Silurian. Looking 

 at the matter in another way : those portions of Tasmania in which 

 the Permo-Carboniferous, Mesozoic and Cainozoic rocks are found 

 at the surface (with the exception of one small region^) carry no 

 primary metalliferous deposits of material importance. 



By the comparison of the age of the ore bodies and that of the 

 associated igneous rocks it has been found that there is a definite 

 time relationship between igneous invasion and ore deposition in 

 many different parts of the world. 



The statement of the historical aspects of oie deposition has 

 been made for America by W. Lindgren,^ for the British Isles by 

 A. M. Finlayson^, for various regions in Europe, Africa and Asia 

 by L. de Launay*, and for Tasmania by W. H. Twelvetrees^. 



In the discussion of this problem there are two rather different 

 aspects which should for some reasons be kept distinct. The 

 author would lay stress on the distinction between the " metalloge- 

 netic epoch " and the " metalliferous province " — the relation in 

 time and the relation in space. This distinction must be borne 



1 The vicinity of Port Cygnet. 



2 " The Gold' Production of North America." Trans. A.I.M.E., Vol. XXXIII., 1903, pp. 

 790-845. Also "Economic Geology," Vol. IV., No. 5, 1909. 



3 Q.J.G.S., Vol. 66, 1910, pp., 281-298 



4 Ibid., literature quoted in foot note, p. 281. 



5 Geol. Surv. Tas., Bulletin No. 9. 



