this is the oldest known coin type, it comes from Asia Minor. Lydian (modern western turkey) a Hellenic city and trading center on the coast of Asia Minor. A 1/6 electrum stater more than 2,700 years old, making it one of the very earliest KNOWN coins. I seriously doubt it IS the oldest type of coin...I BET there are older ones but this, as far as I know, is the oldest type unless things have changed and they found older types and I missed the news.
In the sources you cite, shekels are clearly being used as units of weight measure. The first coin you show is of Alexander the Great, from the low 300's BC. The second is Tyrian shekel from the 1st century BC. (Christians would know this as one of Judas' thirty pieces of silver). I recommend you read Ancient Jewish Coins by Meshorer or Biblical Coinage by David Hendin.
Yes that is a 2nd temple period discovered coin found this week. But I've confirmed this. There was a half shekel coin used for the census and this was recorded in what was called the book of Kings (not the Biblical book Kings) Ruben
Quite a bit out of round (and, to conform to the original poster's request, struck at Londinium) ............... IMP C DIOCLETIANVS PF AVG ................................. PAX AVGGG Issued in the name of Diocletian by Carausius James