Economic geology and history of metallic minerals in the Northern Peninsula of Michigan

The history of exploration of the Ilímaussaq alkaline intrusion is briefly reviewed. Geological and mineralogical investigations were first carried out by K.L. Giesecke in 1806. Later K.J.V. Steenstrup, N.V. Ussing, C.E. Wegmann and a number of others have undertaken studies in and around the intrusion. The intrusion is mainly composed of peralkaline (agpaitic) nepheline syenites and is rich in rare elements and rare minerals. A number of minerals were first discovered in this intrusion, viz. ænigmatite, arfvedsonite, britholite, chalcothallite, epistolite, eudialyte, igdloite (= lueshite), ilimaussite, naujakasite, polylithionite, rinkite, schizolite, sodalite, sorensenite, steenstrupine, tugtupite and ussingite. Renewed geological and mineralogical activity has taken place in Ilímaussaq during the last few years in connection with an examination of the economic geology of the area. A series of publications is in preparation. It was therefore considered to be of some value to present an account of the work until now and to prepare a list of the minerals so far identified and of the papers dealing with the intrusion. The bibliography, together with that prepared by Bøggild (1953), contains the titles of all the papers on the mineralogy, geochemistry and geology of the intrusion known to the writer.

Download Full-text

The Origin of the Porphyry Deposit Name: From Shellfish, Tyrian Purple Dye, and Imperial Rome to the World’s Largest Copper Deposits

SEG Discovery ◽

10.5382/segnews.2019-118.fea ◽

2019 ◽

pp. 1-15

Author(s):

Stewart D. Redwood

Keyword(s):

Economic Geology ◽

Porphyry Copper ◽

Low Grade ◽

Porphyry Copper Deposits ◽

Igneous Petrology ◽

Porphyry Deposit ◽

Copper Deposits ◽

Imperial Rome ◽

Tyrian Purple ◽

History Of

Abstract The porphyry deposit name has a long and fascinating etymological history of over 3,000 years. “Porphyry” is derived from the ancient Greek word porphyra (πoρϕύρα), or purple. It was originally applied to a rare purple dye, Tyrian purple, extracted by the Phoenicians from murex shells. It was later applied to a prized purple porphyritic rock, Imperial Porphyry or Porfido rosso attico, quarried by the Romans from Mons Porphyrites in the Eastern Red Sea hills of Egypt from the first to fifth centuries A.D., and used as a monumental stone in Imperial Rome and Byzantium (Istanbul). The name evolved in the field of igneous petrology to include all rocks with a porphyritic texture, regardless of their color. Mining of the first porphyry copper deposits, which were originally called disseminated or low-grade copper deposits, started in 1905. As a result of the close spatial and genetic relationship to porphyry stocks, they became known as porphyry copper deposits. The term was first used by W. H. Emmons in his 1918 textbook The Principles of Economic Geology, but it was originally used more as an engineering and economic description, as in Parsons’ 1933 book The Porphyry Coppers. It was slow to catch on in the geological literature. It was first used in the title of a paper in Economic Geology in 1947 but did not gain widespread use until the 1970s, following the publication of seminal papers on porphyry models and genesis by Lowell and Guilbert (1970) and Sillitoe (1972, 1973).

Download Full-text