Thornton joined the Holy Blues at the start of November from Guiseley, and will remain with the club for a further month.
He had sustained a broken jaw in pre-season at Guiseley, and made the switch to the BetVictor Northern Premier League side to boost match fitness.
Chadwick, 19, also joined Gainsborough at the start of November and has returned to Hull City after his loan period expired.
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