Extra Large Copper Coin with Sun Yat-Sen's Head and the Republic of China 17th Year （中华民国十七年）. At the back, seems sunlight with Five Ten Pieces of the currency value（伍拾枚）.I have no idea how much that is. 

I don't know it's genuine or modern simulation ,Surely very valuable for collecting. Looks same to me as the Price in China now ￥1688 or more (£168.8 , check online Chinese site)

Diameter:8 cm;

Thick 0.4 cm,

Weight :150 grams.(heavy)