By Andrew Zipkin (Doctoral Candidate, The George Washington University)
Although the main focus of the MEMSAP team during this field season is on the excavations at Chaminade 2 and Mwanganda’s Village, some members of the project have their own specialized research agendas elsewhere in Karonga District. My own focus is on locating geological sources of ochre throughout northern Malawi. Excavations conducted previously in the Karonga area, such as Chaminade 1A, produced evidence of ochre pigment collection and modification. In order to figure out where the ochre originated and how it arrived in an archaeological assemblage, I need to find most or all of the existing deposits of ochre minerals in the Karonga area and build a database of their unique trace element “fingerprints”. Then, at least in theory, it will be possible to match up ochre artefacts to their sources by comparing their fingerprints using statistical software. This sort of approach isn’t particularly new; it has been used for decades to determine the origin of clay pottery and metal alloys, but the application to ochre pigments from Stone Age sites is a relatively recent development since the mid-2000s.
Two days ago, another graduate student, Victor de Moor, and I set off up the Ruasho River which intersects the lakeshore highway just south of Karonga. Victor was investigating the possibility of finding artifact-containing sediments in the hills on either bank of the Ruasho while I was interested in the hills themselves. Most of the ochre I have found in Malawi thus far forms from the weathering of iron-rich igneous and metamorphic rocks. Close to the lakeshore the ground is covered in relatively recent sediments with few exposures of bedrock. However, as you work your way west and inland from the lake, the land rises into hills of gneiss and granite intersected by streams and river beds. My idea is that the best places to seek ochre sources are where bedrock is exposed to consistent water action from a river or stream. This causes the bedrock to weather into different minerals, including iron-rich hematite and goethite (red and yellow ochre).
Although it is the dry season and the Ruasho is a sandy waterless bed about 10 meters wide near Karonga, half a kilometer inland the river bed becomes grassy and swampy and the sand gives way to cattle watering holes and the occasional bathing spot. Following a riverside path along the north bank for about 4 km got us to Malema Camp, a nature preserve we had visited a few days before. Having not seen any archaeology or ochre yet, Victor and I decided to hike back directly through the stream bed along the south bank where a promising looking hill directly abutted the river. Cutting through a banana plantation, we jumped down into the stream bed and started walking east. Within 200 meters I could see that I was on the right track. The hill didn’t just abut the south bank; it was the river bank. The bedrock, glimmering with black mica, continued from near the hill top straight down into the river bed. Ever 50 meters or so a hint of red or yellow staining suggested that weathering was well underway. A sharp blow from a rock hammer was sufficient in each case to peel back the mica and expose the crumbling red and yellow pigment beneath. Chalk up one more source for the Malawi database.