The S&P 500, the Dow Jones and the Nasdaq Composite lost 0.4%, 0.4% and 1.1%, respectively, last week. The world’s largest economy is witnessing a surge in the number of new Delta variant cases in 49 states. This fear weighed on the broader market last week.On a separate note, the U.S. GDP grew at a 6.5% annualized rate in the second quarter of 2021, per the Commerce Department’s first estimate (as mentioned in a CNBC article). However, the metric lagged the Dow Jones estimate of 8.4%.For the week ended Jul 24, 400,000 people filed initial claims for unemployment benefits, above the Dow Jones estimate of 385,000, per a CNBC report. All these reports had a somber effect on Wall Street despite upbeat earnings.Against this backdrop, below we highlight a few ETF areas that were the best performers last week.Clean EnergyAfter riding high in the past year thanks to low rates and Biden’s election win in November, clean energy ETFs have succumbed to a slowdown this year. This acted as an entry point to the clean energy space lately on stimulus sanctions. Notably, among the many policies that Biden and his democratic party support, clean energy is at the forefront. Alpha Architect ETF Trust Viridi Cleaner Energy RIGZ added about 11.8% last week.BlockchainBitcoin, which was downtrodden in the past few weeks, has gained steam on supportive comments from Elon Musk and Cathie Wood. Though bitcoin ETFs are not available to investors, they have blockchain ETFs at their disposal.Bitwise Crypto Industry Innovators ETF BITQ (up 10.8%), Global X Blockchain ETF BKCH (up 8.79%) and Vaneck Digital Transformation ETF DAPP (up 8.76%) are some of the ETFs that were the notable winners.Metal & Mining Rising global demand has been boosting the demand for industrial metals. No wonder,S&P Metals & Mining SPDR XME gained 7% last week.Silver Mining Silver prices remained relatively steady last week on low rates and a downbeat stock market performance. Slight risk-aversion took shape lately. Silver offers a safe-haven trade and benefits from a subdued greenback. It also acts as an industrial metal. With the U.S. economy reopening, this industrial metal is also gaining steam. As a result, SILX gained massively last week. Purefunds ISE Junior Silver ETF SILJ added about 6.8% last week.Rare Earth MetalsRare earth metals are getting a boost from an accelerating shift to new technologies such as electric vehicles. About 27% of rare metals are used in the production of neomagnets, which are the essential components in electric vehicles (EVs). Vaneck Rare Earth Strategic Metals ETF (REMX) was up 6.2% last week.The underlying MVIS Global Rare Earth/Strategic Metals Index tracks the overall performance of companies involved in producing, refining, and recycling of rare earth and strategic metals and minerals. The fund charges 59 bps in fees. 5 Stocks Set to Double Each was hand-picked by a Zacks expert as the #1 favorite stock to gain +100% or more in 2021. Each comes from a different sector and has unique qualities and catalysts that could fuel exceptional growth. Most of the stocks in this report are flying under Wall Street radar, which provides a great opportunity to get in on the ground floor. Today, See These 5 Potential Home Runs >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report SPDR S&P Metals & Mining ETF (XME): ETF Research Reports ETFMG Prime Junior Silver Miners ETF (SILJ): ETF Research Reports VanEck Vectors Rare EarthStrategic Metals ETF (REMX): ETF Research Reports Global X Blockchain ETF (BKCH): ETF Research Reports VanEck Vectors Digital Transformation ETF (DAPP): ETF Research Reports Bitwise Crypto Industry Innovators ETF (BITQ): ETF Research Reports Viridi Cleaner Energy CryptoMining & Semiconductor ETF (RIGZ): ETF Research Reports To read this article on Zacks.com click here. Zacks Investment Research