The Grenville Problem : The Royal Society of Canada Special Publications, No. 1

## PREFACE THE GRENVILLE SUBPROVINCE forms an important part of the Precambrian Shield in eastern Canada. It covers an area 150 to 200 miles wide extending along the southern border of the Shield from Lake Huron to the Labrador coast and projects into the Adirondack region of the United States. It has a total area of about 250,000 square miles of which about 10,000 square miles arc in New York State, 25,000 square miles in Ontario, 177,000 square miles in Quebec, and 38,000 square miles in Labrador. This vast expanse of territory is distinguished from the remainder of the Shield by the presence of extensive areas of crystalline limestone intermingled with a variety of gneisses and highly metamorphosed sedimentary and • volcanic rocks. Because of the great geological complexity and rock alteration the Grenville subprovince presents a variety of problems that have always puzzled and intrigued geologists. A century of investigation has produced much factual information about the distribution of rock types, their relationships, alterations, structure, age, and valuable mineral content. This in turn has led to much speculation as to their mode of origin and relationship to adjacent Precambrian units. Although the Grenville subprovince has not been a prolific source of mineral production when compared with some other major subdivisions of the Shield, it contains the greatest variety of mineral species, and, in recent years, important deposits of iron ore, lead and zinc, uranium, and industrial minerals have been developed. This encouragement has greatly increased the incentive for mineral exploration throughout the whole region. The Grenville subprovince is now undergoing the greatest period of mineral search and development in its entire history. With these facts in mind, the officers of Section IV ( Geology and Allied Sciences) of the Royal Society of Canada decided that it was an opportune time to discuss all aspects of Grenville geology. Accordingly, a symposium on "The Grenville Problem" was arranged for the annual meeting of the Society at Toronto in June, 1955. Geologists with considerable experience in all aspects of Grenville geology were invited to contribute papers and take part in the discussions. They represented mining companies, government surveys, and universities. Thirteen papers were presented and discussed as fully as time would permit. It was felt that this information should be made available to a wider audience, and eventually, through the joint efforts of the Royal Society of Canada and the University of Toronto Press, V vi PREFACE several of the papers presented on that occasion were assembled in this publication. The symposium does not attempt any systematic coverage of the Gren-,•ille rocks nor does it contain contributions from all geologists who have specialized in Grenville geology. Rather, it is a random sampling of areas and topics that are of current interest. It discusses a wide variety of subjects and questions that have come to the fore as geologists delve deeper into the mysteries of the Grenville rocks. They ask : What is the precise meaning of "Grenville" in so far as the term applies to rock types, localities, and concepts? What are the main local units and how are they recognized and differentiated? What is the exact age of the Grenville rock complex? What is its relationship to adjacent subprovinces? What about granitization, intrusion, structure, orogeny? How is the "Grenville front" to be explained? The authors struggle with these and many other problems, often with reference to a specific locality but in some cases dealing with the Grenville as a geological unit. It is not to be expected that students of the Grenville rocks will agree with all that is presented here, but they will be stimulated and impressed by the amount of useful information that patient and systematic field and laboratory work can dig out of a seemingly hopeless rock complex. It is a particular privilege to have papers from two American geologists, Professor A. F. Buddington and Professor A. E. Engel. They have had much experience in the Adirondack region of New York State and are keenly interested in Grenville problems. Their contribution adds much to the value of the symposium. This is the first Canadian attempt to collect some of the available in-• formation and ideas on a difficult and fascinating subject. That it is incomplete and has several omissions is admitted. It is hoped, however, that it will serve a useful purpose and inspire further study and discussions on a geological unit that has a very considerable future potential in the Canadian mineral economy.

THE GRENVILLE SUBPROVINCE forms an important part of the Precambrian Shield in eastern Canada. It covers an area 150 to 200 miles wide extending along the southern border of the Shield from Lake Huron to the Labrador coast and projects into the Adirondack region of the United States. This vast expanse of territory is distinguished from the remainder of the Shield by the presence of extensive areas of crystalline limestone intermingled with a variety of gneisses and highly metamorphosed sedimentary and volcanic rocks. Because of the great geological complexity and rock alteration the Grenville subprovince presents a variety of problems that have always puzzled and intrigued geologists.

A century of investigation has produced much factual information about the distribution of rock types, their relationships, alterations, structure, age, and valuable mineral content. This in turn has led to much speculation as to their mode of origin and relationship to adjacent Precambrian units. Although the Grenville subprovince has not been a prolific source of mineral production when compared with some other major subdivisions of the Shield, it contains the greatest variety of mineral species, and, in recent years, important deposits of iron ore, lead and zinc, uranium, and industrial minerals have been developed. This encouragement has greatly increased the incentive for mineral exploration throughout the whole region. The Grenville subprovince is now undergoing the greatest period of mineral search and development in its entire history.

With these facts in mind, the officers of Section IV (Geology and Allied Sciences) of the Royal Society of Canada decided that it was an opportune time to discuss all aspects of Grenville geology. Accordingly, a symposium on "The Grenville Problem" was arranged for the annual meeting of the Society at Toronto in June, 1955. Geologists with considerable experience in all aspects of Grenville geology were invited to contribute papers and take part in the discussions. They represented mining companies, government surveys, and universities. Thirteen papers were presented and discussed as fully as time would permit. It was felt that this information should be made available to a wider audience, and eventually, through the joint efforts of the Royal Society of Canada and the University of Toronto Press, several of the papers presented on that occasion were assembled in this publication. It is a sampling of areas and topics that are of current interest. It discusses a wide variety of subjects and questions that have come to the fore as geologists delve deeper into the mysteries of the Grenville rocks.

This is the first Canadian attempt to collect some of the available information and ideas on a difficult and fascinating subject. It is hoped, however, that it will serve a useful purpose and inspire further study and discussions on a geological unit that has a very considerable future potential in the Canadian mineral economy.