Any Info on Alloy Composition Appreciated for these Prutot

The closest I could find on these coins of Matthias Antigonus is 70% copper and 27% lead. Does that mean the rest is Tin? Do any Judaean experts have any more info on the metallic composition of these unusual coins? The numbers above (4 prutah)
are from this study: http://www.ins.org.il/files/files/Mattathias Antigonus coins-the last king of the Hasmonean .pdf
(8 prutah)