Complex sentence: Congress also mandated 45,000,000 part-silver pieces be struck for collectors; the Mint sold over half of these before melting the remainder after withdrawing them from sale in 1986.
Split into simpler sentences: Congress also mandated 45,000,000 part-silver pieces be struck for collectors. The Mint sold over half of the part-silver coins before melting the remainder after withdrawing them from sale in 1986.