Mumbai, May 13 -- Hindustan Zinc Ltd gained 4.72% today to trade at Rs 671.8. The BSE Metal index is up 1.42% to quote at 42588.87. The index is up 4.76 % over last one month. Among the other constituents of the index, Steel Authority of India Ltd increased 3.75% and National Aluminium Company Ltd added 1.59% on the day. The BSE Metal index went up 42.75 % over last one year compared to the 8.01% fall in benchmark SENSEX. Hindustan Zinc Ltd has added 19.41% over last one month compared to 4.76% gain in BSE Metal index and 2.86% drop in the SENSEX. On the BSE, 1.14 lakh shares were traded in the counter so far compared with average daily volumes of 3.61 lakh shares in the past one month. The stock hit a record high of Rs 732.6 on 28 Jan 20...