IPO - Jupiter Mines Limited, page-155

CabinetMember, you are incorrect when you say " even if the alloy prices rise, the smelters' profits are limited to a 15% margin or so"
The smelter profits are in fact closer to 24% currently. It is actually easy to see the profits that the OM Sawarak smelter makes due to its Malaysian partners Financials which are published quarterly and shows the Quarterly profit distribution. http://cmsb.com.my/investor-relations/reports/quarterly-reports/
Last quarter 2017 CMSB made $10 million profit and  so OMH $30 million profit on OM Sarawak. ie Now OMH share of OM Sarawak  with $500 million pa sales we have $120 million profits. ( Close to 24% profits)
I do agree that they are different businesses, OMH is a miner and a smelter, JMS is a 49.9% partner in one mine. JMS is as you say more geared to increases in Mn ore prices, but then again the ferro alloy business is also a  profitable business to be in. Look at S32, they have smelters in Australia and South Africa.
I will happily bet that OMH is at $2/share before JMS is at $1/share.