Pallasite, PMG-as (main-group, anomalous silicate composition)
standby for springwater photo
Recognized Summer, 1931
52° 0' N., 108° 18' W.

Three masses weighing 85, 41, and 23 pounds, having a combined weight of 149 pounds, were found in a field 100 miles west of Saskatoon in Saskatchewan, Canada. One of the masses was sent by the finder to the Nininger Meteorite Laboratory in Denver where it was verified as being meteoritic. The 117 pound (52 kg) main mass was found by Mike Farmer and team members in their 2009 expedition.

Springwater has anomalous compositions with respect to olivine fayalite, Sc, Cr, Mn, Zn, and phosphate REE contents. It has a phosphoran olivine composition distinct from most other main-group pallasites, and many of its anomalous chemical compositions suggest that it crystallized from a late-stage, P-enriched, Si-depleted melt which cooled quickly through high temperatures (Boesenberg et al., 2004). In contrast, it has a Sc content that is the lowest among pallasites, and which is consistent with a minimally evolved melt (Mittlefehldt and Rumble, III (2006). The mineral farringtonite was first found in this meteorite. Springwater silicates do not follow an igneous fractionation trend, but instead are more consistent with the loss of Fe through oxidation as a magmatic gas phase was introduced (Wasson and Choi, 2003). These oxidizing gases were concentrated in voids formed by core contraction and mantle collapse during cooling, and they introduced enrichments of the volatile siderophiles Ge and Ga into various pallasitic lithologies.

Springwater and the other PMG-as members might have formed in a more chemically heterogeneous mantle region than normal PMG members, though overall compositional and isotopic similarities still suggest a common parent body for all. It has been proposed that main-group pallasites could represent melt residues of the IIIAB iron parent body. However, due to the significantly slower cooling experienced by main-group pallasites compared to IIIAB irons, as well as the younger ages determined for main-group pallasites, a common parent body is not considered plausible by some (E. Scott, 2007). Moreover, pallasites have a much younger range of CRE ages than the IIIAB irons (Huber et al., 2011), although this may be explained by the higher space endurance of the irons.

Formation scenarios and classification schemes for the main-group pallasites can be found on the Imilac page. In the photo below is a large etched slice of Springwater exhibiting the typical distribution of silicate and metal, shown courtesy of Sergey Vasiliev.

standby for springwater photo
Photo courtesy of Sergey Vasiliev—SV-meteorites.com