John F. H. Thompson

Absolute timing of sulfide and gold mineralization: A comparison of Re-Os molybdenite and Ar-Ar mica methods from the Tintina Gold Belt, Alaska

New Re-Os molybdenite dates from two lode gold deposits of the Tintina Gold Belt, Alaska, provide direct timing constraints for sulfide and gold mineralization. At Fort Knox, the Re-Os molybdenite date is identical to the U-Pb zircon age for the host intrusion, supporting an intrusive-related origin for the deposit. However, 40Ar/39Ar dates from hydrothermal and igneous mica are considerably younger. At the Pogo deposit, Re-Os molybdenite dates are also much older than 40Ar/39Ar dates from hydrothermal mica, but dissimilar to the age of local granites. These age relationships indicate that the Re-Os molybdenite method records the timing of sulfide and gold mineralization, whereas much younger 40Ar/39Ar dates are affected by post-ore thermal events, slow cooling, and/or systemic analytical effects. The results of this study complement a growing body of evidence to indicate that the Re-Os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems.

Triassic-Jurassic silica-undersaturated and silica-saturated alkalic intrusions in the Cordillera of British Columbia: Implications for arc magmatism

Alkalic igneous rocks of early Mesozoic age are found in both the Quesnel and Stikine terranes in the Canadian Cordillera and include both silica-undersaturated and silica-saturated types. The saturated complexes are most abundant in Quesnellia and are multiphase complexes dominated by monzonite to diorite intrusions. Undersaturated complexes are distributed through both terranes, are dominated by syenite with lesser monzonite and pyroxenite, and, when present as a single intrusion, are characterized by concentric zoning, igneous layering, and planar mineral fabrics. Both types of complex are associated with Cu-Au mineralization accompanied by potassic and distinctive sodic and calc-potassic alteration assemblages. Although undersaturated and saturated alkalic intrusions are petrographically distinct, a petrogenetic association is suggested by their spatial coincidence in some districts, and similarities in their tectonic environment and associated alteration. The undersaturated complexes represent a distinctive suite of alkalic intrusion with magmatic arc affinities, and their emplacement into both Stikinia and Quesnellia between 210 and 200 Ma suggests that these terranes were either linked at that time or have shared unusual but similar magma-generating tectonic events at identical times.

One Hundredth Anniversary Volume

From the first issue in 1905 onward, Economic Geology has been the main publication for those who study mineral deposits; indeed, it is now difficult to imagine economic geology without Economic Geology. It is interesting to ask, therefore, Who were the farsighted people who founded the journal, and Why did they think a specialized publication devoted to mineral deposits was needed? Let us first address the question, Who were the founders? They were the 12 men who collectivelydecided a new publication was needed, who then planned the financial structure to support the venture, and who served as the original editorial group. All were employed by, or associated with, the U.S. Geological Survey. Josiah Edward Spurr suggested the need for a journal sometime in November or December 1904. After informal discussions, nine of the founders met in the office of Waldemar Lindgren in the headquarters of the U.S. Geological Survey in Washington, D.C., on May 16, 1905, and founded the Economic Geology Publishing Company. The sole purpose of the company was the publication of a journal ‘...devoted primarily to the broad application of geologicprinciples to mineral deposits of economic value, and to the scientific description of such deposits, and particularly to the chemical, physical, and structural problems bearing on their genesis.’ Initial financing for the new company was raised by the sale of 80 shares at a cost of

Intrusion-related gold deposits associated with tungsten-tin provinces

25 per share. Eight of the men at the founding meeting formed the first board of directors; Spurr was president, Frederick L. Ransome, secretary, and George O. Smith, treasurer. Other members were Arthur H. Brooks, Marius R. Campbell, Walter H. Weed, Waldemar Lindgren, and a young academic from Lehigh University in Pennsylvania, John D. Irving. Theninth man at the meeting was H. Foster Bain. Irving was appointed editor. Lindgren, Ransome, and Campbell from the U.S. Geological Survey, together with three academics, James F. Kemp of Columbia University, Heinrich Ries ofCornell University, and Charles K. Leith of the University of Wisconsin, were appointed associate editors. The initial board members, the editor, and associate editors are the people we now recognize as the founders of Economic Geology. Two others, Frank D. Adams, of McGill University in Canada, and John. W. Gregory, of Glasgow University in Scotland, were subsequently added as associate editors, and a third person, W. S. Bayley of the University of Illinois, was appointed as business editor, but