Prehistoric quarry investigations have long posed problems for archaeologists. The plans and development histories of prehistoric bedrock quarries (in contrast to isolated quarry workshops or "knapping stations") have not been widely studied in eastern North America, and so there is a general lack of familiarity with this type of site. Often, these sites are ignored because the archaeologist is unaware it exists! Even when bedrock quarries are identified in the field, however, archaeological investigations will often focus upon the excavation of reduction sequences for the simple reason that reduction sequences can be approached using traditional methods. However, reduction sequences may occur anywhere from several meters to several kilometers from quarry faces, so the investigation of reduction sequences does not illuminate quarrying and quarry-related activity as a whole.

To address this problem, La Porta & Associates has developed a combination mass and attribute analysis method for investigating bedrock quarries. Our methodology is based upon a mineral resource approach to ore evaluation that tackles both extraction technology and mine tailings analysis directly. Although elements of the mineral resource approach have been employed in European studies of prehistoric quarries, this methodology has never before been applied in the United States, and as such represents a significant contribution to archaeological field methodologies for investigating both prehistoric and historic mining sites.

We have developed hierarchical classification schemes for features of a prehistoric quarry landscape, as well as the individual components of a quarry, which are based upon concepts from the field of economic geology. Under the classification scheme for quarry landscapes, groups of prehistoric quarries are generally clustered within metallogenic provinces. Those provinces are divided into districts according to their structural history. All quarries identified within a district are referred to as motions; the smaller-scale attempts at mining, both failed and successful, are the movements within a motion. All prospecting attempts are referred to as expressions. The quarries themselves are divided into zones of extraction, milling stations, processing areas, zones of benficiation, and refinement sequences. All of these have a spatial distribution within the quarries that defines common practices of the economics of ore extraction. A mineral resource approach to investigating prehistoric quarries offers a number of advantages over traditional archaeological methods. These advantages include:

The ability to construct a predictive model for quarry distribution on the landscape, utilizing geologic mapping and (if available) analysis of drill cores and/or seismic data. Predictive models are especially useful for longitudinal studies. The ability to make measurements and gather data from bare rock surfaces, especially on steep slopes, as well as from non-portable objects such as quarry faces and large ore blocks. Standard archaeological practices are not designed to take such information into account. The ability to define morphological and petrological hammerstone types and to associate those types with classes of mine tailings as well as an inferred function. The combined analysis of mine tailings and hammerstone types will serve to elucidate the systematic manufacturing stages present in quarries to a degree not achieved through standard archaeological practices. A well-defined terminology for mining products that relates clearly to manufacturing processes and task subdivision (the chain of operation), in contrast to the current terminology (e.g. block, chunk, shatter, waste flake and trim) which does not. The ability to quantify the control that petrofabric (e.g., domainal cleavage, close-spaced jointing) and diagenesis exert on stone tool production and stone tool technology. This information can provide answers to key research questions concerning the artifacts and activities present in prehistoric quarries, but as this particular technique requires a level of familiarity with geologic field methods not normally possessed by archaeologists, it is not part of a standard field investigation of quarries.

La Porta & Associates is the only firm currently qualified to conduct prehistoric bedrock quarry investigations using this economic mineral resource approach. If you have a bedrock quarry on your site, or you think you might have one, give us call - we would be happy to assist you.